Primary prevention

Vaccines

  • The World Health Organization (WHO) has authorised the use of the following vaccines for global use:[338][339][340][341][342][343][344]

    • mRNA vaccines: Comirnaty® (Pfizer/BioNTech); Spikevax® (Moderna)

    • Adenovirus vector vaccines: Vaxzevria® (AstraZeneca); Ad26.COV2.S (Janssen)

    • Protein subunit vaccines: Nuvaxoid® (Novavax); Covovax® (Serum Institute of India)

    • Inactivated virus vaccines: Covilo® (Sinopharm); CoronaVac® (Sinovac)

    • WHO: COVID-19 vaccines technical documents Opens in new window

  • Vaccine availability and immunisation programmes differ between countries.

    • Other vaccines have been authorised in specific countries (e.g., Valneva inactivated virus vaccine in the UK). Vaccines are generally available under emergency-use, provisional, or conditional marketing authorisations, but may be fully approved in some countries. Consult your local guidance for information.

  • Patients must give informed consent prior to vaccination.

    • For consent to immunisation to be valid, it must be given freely, voluntarily, and without coercion by an appropriately informed person.[345]

  • Protection starts around 7 to 14 days after full vaccination (depending on vaccine brand).

    • Check your local guidance for when vaccine protection starts. Duration of protection is unknown and is still being assessed in ongoing clinical trials.

    • Have a high level of suspicion of reported symptoms post-vaccination, and avoid dismissing complaints as vaccine-related until vaccine recipients are tested and true infection is ruled out.[346]

  • Breakthrough infections are possible. Vaccinated people should continue to follow local public health recommendations.

    • Breakthrough infections that have resulted in hospitalisation or death, as well as mild or asymptomatic infections, have been reported in fully vaccinated people.[347] Vaccinated people should therefore be considered a possible source of transmission.[348] Vaccinated people are more likely to experience breakthrough infections more than 3 months after the second vaccine dose.[349]

    • Breakthrough infections have been reported with the Omicron variant, including people who received a booster dose.[350] While breakthrough infections with the Omicron variant are more frequent compared with the Delta variant, hospital admissions were less frequent with Omicron.[351]

    • Risk factors for breakthrough infection after the first dose may include frailty in older adults ≥60 years, dementia, living in deprived areas, immune dysfunction, cancer (especially haematological malignancies and those undergoing active cancer care), and obesity.[352][353][354][355][356] Older age, male sex, increasing number of comorbidities, hospitalisation in the previous 4 weeks, high-risk occupation, care home residence, socioeconomic deprivation, and smoking history were all associated with an increased risk of hospitalisation or death in patients with breakthrough infections after the first dose.[357] Prior infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may be associated with a lower risk for breakthrough infection.[358]

    • One small observational study in patients admitted to hospital with a positive test found that 46% of fully vaccinated people with breakthrough infection were asymptomatic, while 26% had severe or critical disease, 20% had moderate disease, and 7% had mild disease.[359] In another study, the rate of severe disease or death per 1000 person-days was 4.08 among those with breakthrough infections and 3.6 among unvaccinated matched controls with infection.[360]

    • Emerging evidence indicates that fully vaccinated people with breakthrough infections have similar viral loads of the Delta variant compared with unvaccinated people, and are therefore equally likely to transmit the infection, including to fully vaccinated contacts.[361][362] The secondary attack rates among household contacts exposed to fully vaccinated index cases was similar to household contacts exposed to unvaccinated index cases (25% for vaccinated versus 23% for unvaccinated).[363]

Vaccines: dose schedules

  • The primary vaccination series consists of either a two-dose or one-dose schedule depending on the vaccine used (see table below).

    • Dose intervals for the two-dose series may differ between countries depending on vaccine coverage rates and supply constraints.

    • The WHO and the US Centers for Disease Control and Prevention recommend 3 weeks (Pfizer/BioNTech vaccine) or 4 weeks (Moderna vaccine) to 8 weeks between the first and second doses of mRNA vaccines. An interval of 8 weeks is preferred as this interval is associated with higher vaccine efficacy and a lower risk of myocarditis (e.g., in young men). However, there may be some groups who require quick protection (e.g., high-risk groups, settings of high transmission intensity).[338][339][364]

  • Additional doses are recommended as part of the primary vaccination series for immunocompromised people.

    • The WHO recommends that the primary vaccination series for all vaccines should be extended to include an additional dose in moderately to severely immunocompromised people aged ≥5 years. The additional dose should be given at least 1 month and within 3 months after the primary series (or at the earliest opportunity if more than 3 months have elapsed). The most appropriate timing for the additional dose may vary depending on the epidemiological setting and the timing and extent of the immunosuppressive therapy the patient is receiving. A homologous additional dose is standard practice, but alternative heterologous regimens for the additional dose may also be considered, taking into account current vaccine supply, vaccine supply projections, and other access considerations.[365] The Pfizer/BioNTech vaccine is recommended in children aged 5 to 11 years.[338]

    • In the UK, the Joint Committee on Vaccination and Immunisation (JCVI) recommends an additional dose in severely immunocompromised people aged ≥5 years, at least 8 weeks after the second dose, with special attention paid to current or planned immunosuppressive therapies. Choice of vaccine depends on the person’s age and the vaccine used for the primary series. The Pfizer/BioNTech vaccine is preferred in those aged 5 to 17 years.[366][367]

    • In the US, the Centers for Disease Control and Prevention recommends an additional dose in moderately or severely immunocompromised people aged ≥5 years (Pfizer/BioNTech vaccine) or ≥18 years (Moderna vaccine), at least 4 weeks after completion of the primary vaccination series. In those who receive a primary Janssen vaccine dose, a second (additional) dose using an mRNA vaccine is recommended at least 4 weeks after the first dose.[364]

    • There are no vaccine efficacy studies following a third dose in immunocompromised people.[368] Although there is no direct evidence that the ability to produce antibodies in these patients offers protection, it is expected that the extra dose increases protection, at least in some patients. The risk of adverse effects after an additional dose is not known and is being monitored.[369]

  • Booster doses are recommended after the primary vaccination series.

    • The WHO recommends that the introduction of booster doses should be firmly evidence-driven and targeted to the population groups at highest risk of serious disease and those necessary to protect the health system.[370] A booster dose is recommended for the highest priority-use groups 4 to 6 months after the completion of the primary series. Once high booster dose coverage has been achieved in these groups, a booster may be considered for other lower priority-use groups. If more than 6 months have elapsed since completion of the primary series, the booster dose should be given at the earliest opportunity. The need for booster doses in children aged 5 to 11 years has not yet been determined.[338][339] A vaccination strategy based on repeated booster doses of the original vaccine composition is unlikely to be appropriate or sustainable.[371]

    • In the UK, the JCVI recommends that all people aged ≥16 years should be offered a first booster dose at least 3 months after the completion of the primary course. Severely immunosuppressed people should be offered a booster dose with a minimum of 3 months between the third primary and booster dose. A booster should also be offered to people aged 12 to 15 years who are in a clinical risk group or who are a household contact of someone (of any age) who is immunosuppressed, or who are severely immunocompromised and who have had a third primary dose. Both the Pfizer/BioNTech and Moderna vaccines should be used with equal preference.[372][373] Boosters in children aged 12 to 15 years who are not at high risk and in those aged 5 to 11 years will be reviewed in due course.[367] Another (second) booster dose is recommended in adults aged ≥75 years, residents in care homes, and people ≥12 years who are immunosuppressed, around 6 months after the last dose, in March to May (Spring) 2022.[374]

    • In the US, the Centers for Disease Control and Prevention recommends that all people aged ≥12 years should receive a first booster dose. Recipients of an mRNA primary series should receive a booster dose at least 5 months after completing their primary series (at least 3 months in people who are moderately or severely immunocompromised). Recipients of a Janssen primary series should receive a booster dose at least 2 months after completing their primary series. Any of the vaccines can be used for booster vaccination, regardless of the vaccine used for the primary series. However, an mRNA vaccine is preferred over the Janssen vaccine for booster vaccination, and only the Pfizer/BioNTech vaccine is recommended in adolescents aged 12 to 17 years. Another (second) booster dose of an mRNA vaccine may be considered at least 4 months after the first booster dose in people aged ≥12 years who are moderately or severely immunocompromised, and all adults aged ≥50 years. People aged ≥18 years who are not moderately to severely immunocompromised and who received a Janssen vaccine for their primary series and booster dose may receive a second booster dose using an mRNA vaccine at least 4 months after the first Janssen vaccine booster dose. Booster doses of Pfizer/BioNTech and Janssen vaccines are the same as the primary series. However, the booster dose of the Moderna vaccine is half the dose used for the primary series. In moderately or severely immunocompromised people, the booster doses are the fourth or fifth doses as there are 3 doses in the primary series.[364]

    • The European Centre for Disease Prevention and Control and the European Medicines Agency’s COVID-19 task force have concluded that it is too early to consider using a second booster of mRNA vaccines in the general population as there is currently no clear evidence that vaccine protection against severe disease is waning substantially in adults with normal immune systems aged up to 79 years. However, both agencies agree that a second booster can be given to adults ≥80 years of age due to the higher risk of severe disease in this age group.

    • Evidence for the benefit of a first booster dose is inferred through immunogenicity, and the overall level of certainty is very low for prevention of symptomatic disease, hospitalisation, and death, as well as serious adverse events and reactogenicity.[375] In the ongoing, placebo-controlled, randomised, phase 3 trial, a booster dose administered a median of 10.8 months after the second dose provided 95.3% efficacy compared with two doses during a median follow-up of 2.5 months. No new safety signals were identified.[376] Observational data to support the safety and efficacy of booster doses are emerging, but their follow-up periods are too short to assess long-term effectiveness, and the number of trial participants is small.[377][378][379][380][381][382][383][384] The studies also focus on plasma neutralising antibodies and don’t take into account the protection provided by cellular immunity. More data are needed to understand the potential impact of booster vaccination on the duration of protection against severe disease, mild disease, infection, and transmission, particularly in the context of emerging variants.[370]

    • Evidence for the benefit of a second booster dose is emerging and comes largely from Israel.[385][386][387] Approval of a second booster dose by the US Food and Drug Administration was based on a summary of safety surveillance data provided to the agency by the Ministry of Health of Israel.[388]

    • There are currently no data available on the efficacy of booster doses for inactivated whole-virus vaccines.[389]

  • Heterologous vaccination schedules may be recommended in some countries.

    • The WHO recommends that homologous schedules should be considered standard practice. However, a flexible approach is supported, and two heterologous doses of any authorised vaccine may be used to be a complete primary series. Heterologous vaccination should only be implemented with careful consideration of current vaccine supply, vaccine supply projections, and other access considerations, alongside the potential benefits and risks of the specific products being used. The relative risks and benefits of homologous versus heterologous primary and booster doses will continue to be reviewed.[390]

    • Cohort studies have found that heterologous vaccination schedules induce a robust humoral and cellular immune response after a second dose of an mRNA vaccine in people primed with the AstraZeneca vaccine 8 to 12 weeks earlier, and were associated with an acceptable and manageable reactogenicity profile.[391][392][393][394][395] However, some studies have found an increase in transient systemic reactogenicity after the boost dose of an mRNA vaccine in heterologous vaccine schedules in comparison to homologous vaccine schedules in participants aged 50 years and older.[396][397][398] The difference between studies may be explained, in part, by the difference in administration intervals used between the studies (i.e., 28 days versus 8-12 weeks).

    • The European Medicines Agency and the European Centre for Disease Prevention and Control have published guidance on when to use heterologous schedules for the primary vaccination series and booster doses.[399]

  • Consider administering COVID-19 vaccines and influenza vaccines together.

    • The WHO recommends that coadministration of any dose of a COVID-19 vaccine with an inactivated seasonal influenza vaccine is acceptable and may be considered during the same visit. Only limited evidence exists to support this recommendation, but available evidence does not show increased adverse events. The WHO recommends using the contralateral limb for injection when the two vaccines are administered during the same visit to minimise any perceived risk, and monitoring for adverse effects after. No coadministration data are available for other live or inactivated vaccines.[400]

    • In the UK, the JCVI advises that COVID-19 vaccines and influenza vaccines may be administered together where operationally practical, although there are a lack of data to support this.[401]

    • In the US, the National Institutes of Health recommends deferring influenza vaccination in patients with symptomatic COVID-19 until the patient has completed their isolation period and they are no longer moderately or severely ill. It also recommends deferring influenza vaccination in patients with asymptomatic or mild COVID-19 until the patient has completed their isolation period.[19]

    • A multicentre randomised controlled phase 4 trial found that concomitant COVID-19 and influenza vaccine administration raised no safety concerns, most systemic reactions were mild or moderate, and the immune response was not adversely affected.[402] Similar results have been reported in an ongoing phase 2, open-label trial in older adults.[403]

  • Consult your local guidelines for detailed information on dose schedules.

<11 years

12-17 years

≥18 years

Comirnaty® (tozinameran)

Pfizer/BioNTech

Pfizer/BioNTech COVID-19 vaccine SmPC Opens in new window

mRNA vaccine

5-11 years: 0.2 mL (10 micrograms) IM; second dose at least 21 days after [orange cap formulation]

0.3 mL (30 micrograms) IM; second dose at least 21 days after [purple cap formulation]

Spikevax® (elasomeran)

Moderna

Moderna COVID-19 vaccine SmPC Opens in new window

mRNA vaccine

6-11 years: 0.25 mL (50 micrograms) IM; second dose at least 28 days after

0.5 mL (100 micrograms) IM; second dose at least 28 days after

Vaxzevria®

AstraZeneca

AstraZeneca COVID-19 vaccine SmPC Opens in new window

Adenovirus vector vaccine

Not currently authorised for use

0.5 mL IM; second dose 4-12 weeks after

Nuvaxovid®

Novavax

Novavax vaccine SmPC Opens in new window

Protein subunit vaccine

Not currently authorised for use

0.5 mL (5 micrograms) IM; second dose 3 weeks after

Ad26.COV2-S

Janssen

Janssen COVID-19 vaccine SmPC Opens in new window

Adenovirus vector vaccine

Not currently authorised for use

0.5 mL IM as a single dose

VLA2001

Valneva

Valneva vaccine SmPC Opens in new window

Inactivated virus vaccine

Not currently authorised for use

0.5 mL (5 micrograms) IM; second dose at least 28 days after

Primary vaccination series for authorised vaccines in the UK (based on age groups). Information is taken from the UK Summary of Product Characteristics (SmPC; see links in table). Two formulations of the Pfizer/BioNTech vaccine are available: a 10 micrograms/dose concentrate authorised for 5-11 year olds only; and a 30 micrograms/dose concentrate for children ≥12 years of age and adults. The dose of the Moderna vaccine for 6- to 11-year-olds is half of the dose for individuals ≥12 years of age. Additional doses and booster doses may be recommended in addition to the primary vaccination series; see the Vaccines: dose schedules section above. Dose schedules may differ in some locations; consult your local guidance. Last updated: 12 May 2022

Vaccines: contraindications

  • A history of anaphylaxis or hypersensitivity to any component of the vaccine is a contraindication to vaccination. If anaphylaxis occurs after the first dose, a second dose of the vaccine should not be administered.[338][339][340][341][342][343][344] In addition to this, people who have had thrombosis with thrombocytopenia syndrome following the first dose of the AstraZeneca vaccine should not receive a second dose of the vaccine.[340]

  • Other contraindications may apply to specific vaccines in different countries. For example, in the UK, the AstraZeneca and Janssen vaccines are contraindicated in people with a history of capillary leak syndrome, and a further dose of the AstraZeneca vaccine should not be given to those who experienced transverse myelitis after a previous dose (see Summary of Product Characteristics links above). Consult your local guidance for more information.

  • Use caution in people receiving anticoagulant therapy or those with bleeding disorders due to the risk of bleeding or bruising with intramuscular injections.

  • In the US, the Janssen vaccine has been limited to use in certain people. The Food and Drug Administration has limited the authorised use of the Janssen vaccine to individuals ≥18 years of age for whom other authorised or approved COVID-19 vaccines are not accessible or clinically appropriate, and to individuals ≥18 years of age who elect to receive the Janssen vaccine because they would otherwise not receive a COVID-19 vaccine. The agency has determined that the risk of vaccine-induced immune thrombocytopenia and thrombosis (see Vaccines: adverse events below) warrants limiting the authorised use of the vaccine.[404]

Vaccines: adverse events

  • Myocarditis and pericarditis

    • Myocarditis or pericarditis may occur following vaccination with mRNA vaccines.[405] It has been postulated that mRNA vaccines may increase inflammation on the endothelium and T-cell infiltration of cardiac muscle, but further research is required.[406] Cases have also been reported with adenovirus vector vaccines, albeit more rarely.[407]

    • Estimates of incidence vary. In the UK, 18 cases of myocarditis per million doses have been reported with the Moderna vaccine and 10 cases per million doses with the Pfizer/BioNTech vaccine across all ranges after first, second, and third doses, according to the Yellow Card reporting system (as of 20 April 2022). The incidence of pericarditis is slightly lower (10 cases per million doses for Moderna, and 7 cases per million doses for Pfizer/BioNTech). Rates of myocarditis and pericarditis are highest in the 18-to-29-years age group (29 cases per million doses after the second dose of the Pfizer/BioNTech vaccine, and 69 cases per million doses after the second dose of the Moderna vaccine). There appears to be an increased risk after the third dose (booster), but data is still emerging and the risk may be lower than after the second dose.[408][409] In the US, monitoring by the Vaccine Adverse Event Reporting System (VAERS) detected 70.7 cases of myocarditis per million doses in males aged 12 to 15 years after the second dose, 105.9 cases per million doses in males aged 16 to 17 years, and 52.4 to 56.3 cases per million doses in males aged 18 to 24 years (as of 30 September 2021).[410] Estimates are based on data from passive surveillance systems so the true number of cases may be higher.

    • Cases occur predominantly in adolescents and young adults (median age of onset 21 years), more often in males than in females, more often following the second dose, and typically within 3 days after vaccination (up to 25 days).[411] In a cohort study of 23.1 million residents aged ≥12 years across four Nordic countries, the risk of myocarditis was higher within 28 days of vaccination with both mRNA vaccines compared with being unvaccinated. The risk was highest within the first 7 days of being vaccinated, was increased for all combinations of mRNA vaccines, and was more pronounced after the second dose (with young males aged 16-24 years having the highest risk).[412]

    • Consider the diagnosis in children, adolescents, or adults with new-onset and unexplained significant chest pain, tachycardia or tachypnoea, dyspnoea, palpitations, dizziness or syncope, or general clinical concern, within 10 days of vaccination. Order a 12-lead electrocardiogram, inflammatory blood markers, and troponin. If any of these investigations are abnormal, discuss the management plan with the cardiology team.[413]

    • UK Health Security Agency: myocarditis and pericarditis after COVID-19 vaccination - clinical management guidance for healthcare professionals Opens in new window

    • The short-term clinical course appears to be mild in most patients, but the long-term risks remain unknown.[414]

    • In the UK, the UK Health Security Agency recommends that if there is no evidence of ongoing myocarditis at the 8-week follow-up, people may be offered vaccination with the Pfizer/BioNTech vaccine from 12 weeks after their last dose if further doses are due. An individual risk-benefit assessment is recommended if there is evidence of ongoing effects of acute or subacute myocarditis at the 8-week follow-up.[413]

    • In the US, the Centers for Disease Control and Prevention recommends that people with a history of myocarditis or pericarditis after a dose of an mRNA vaccine should generally avoid a subsequent dose of any COVID-19 vaccine. If the decision is made to administer a subsequent dose after a risk assessment is made, the person should wait until at least after the episode has resolved.[364]

  • Guillain-Barre syndrome

    • Guillain-Barre syndrome may occur following vaccination with adenovirus vector vaccines. Cases have also been reported with mRNA vaccines, albeit more rarely.[415][416]

    • Estimates of incidence vary. In the UK, 495 cases of Guillain-Barre syndrome and 29 cases of Miller Fisher syndrome have been reported with the AstraZeneca vaccine, 102 cases of Guillain-Barre syndrome and 5 cases of Miller Fisher syndrome have been reported with the Pfizer/BioNTech vaccine, and 17 cases of Guillain-Barre syndrome have been reported with the Moderna vaccine (as of 20 April 2022).[408] In the US, monitoring by VAERS detected 1 case of Guillain-Barre syndrome per 100,000 doses of the Janssen vaccine (as of 24 July 2021). The median time to onset following vaccination was 13 days (range 10-42 days), and 93% of cases were serious.[417]

  • Vaccine-induced immune thrombocytopenia and thrombosis (VITT)

    • VITT may occur following vaccination with adenovirus vector vaccines.[418] Cases have also been reported with mRNA vaccines, albeit more rarely.[419]

    • Estimates of incidence vary. In the UK, 15.7 cases per million doses have been reported after first or unknown doses of the AstraZeneca vaccine (21.4 per million in people aged 18-49 years), and 2.1 cases per million doses have been reported after the second dose, with a case fatality rate of 18% (as of 20 April 2022).[408] In the US, the overall risk with the Janssen vaccine has currently been estimated to be 3.83 cases per million people who receive the vaccine, with the reporting rate highest among women aged 30 to 39 years (10.6 cases per million doses) and 40 to 49 years (9.02 cases per million doses), with a case fatality rate of 15%.[420]

    • Some countries have implemented age-related prescribing restrictions for adenovirus vector vaccines. In the UK, the JCVI advises that it is preferable for adults aged <40 years without underlying health conditions to receive an alternative to the AstraZeneca vaccine if possible.[421] In the US, the Janssen vaccine has been limited to use in certain people due to the risk of VITT (see Vaccines: contraindications above).[404] Consult your local guidance.

    • The World Health Organization recommends that people who have had VITT following the first dose of the AstraZeneca vaccine should not receive a second dose of the same vaccine.[340] A small cohort study found that none of the 40 patients who experienced VITT after their first dose of the AstraZeneca vaccine had any relapse of symptoms or severe adverse reactions after receiving their second dose, regardless of the vaccine received. However, the majority of people received the Pfizer/BioNTech vaccine as their second dose.[422]

    • Use caution in people with a history of heparin-induced thrombocytopenia or cerebrovascular venous and sinus thrombosis. The US Centers for Disease Control and Prevention recommends that people with a history of an episode of an immune-mediated syndrome characterised by thrombosis and thrombocytopenia, such as heparin-induced thrombocytopenia, should be offered an mRNA vaccine instead of an adenovirus vector vaccine.[364]

    • There is a link to rare cases of venous thromboembolism that is distinct from VITT, and cerebral venous sinus thrombosis without thrombocytopenia with adenovirus vector vaccines.[423][424] A retrospective cohort study found that vaccination with the AstraZeneca vaccine was associated with a small excess risk for deep vein thrombosis.[425]

    • See the Complications section for more information on VITT, including diagnosis and management.

  • Anaphylaxis

    • Severe allergic reactions, including anaphylaxis, may occur after vaccination. Reactions may be due to the presence of lipid pegylated ethylene glycol (PEG), or PEG derivatives such as polysorbates.[426]

    • Globally, the pooled incidence of post-vaccination anaphylaxis has been estimated to be between 5.58 to 7.91 cases per million doses based on available data, and depends on the vaccine used.[427][428] However, rates as high as 32 per million doses (Moderna) and 38 per million doses (Pfizer/BioNTech) have been reported.[429]

    • A history of anaphylaxis to any component of the vaccine is a contraindication to vaccination. People who have an anaphylactic reaction following the first dose of the vaccine should not receive a second dose of the same vaccine. Observe people for 15 to 30 minutes after vaccination in healthcare settings where anaphylaxis can be immediately treated.[338][339][340][341][342][343][344] Some countries have removed the requirement for the observation period following vaccination in certain people. Consult local guidelines for recommendations on vaccinating people with a history of allergies or anaphylaxis.

    • A systematic review and meta-analysis of case studies and case reports found that the risk of immediate allergic reactions, including anaphylaxis, associated with a second dose of an mRNA vaccine was low among people who experienced an immediate allergic reaction to the first dose.[430]

  • Immune thrombocytopenia

    • Immune thrombocytopenia may occur following vaccination with adenovirus vector vaccines. Use caution in people with a history of a thrombocytopenic disorder. People with a history of a thrombocytopenic disorder should have their platelets monitored for the first 4 weeks following vaccination.[423]

    • Estimates of incidence vary. In the UK, 4 cases per million doses have been reported with the AstraZeneca vaccine (as of 20 April 2022). Approximately 10% to 20% of cases had a history of immune thrombocytopenia or an underlying condition known to be associated with immune thrombocytopenia.[408]

  • Transverse myelitis

    • Transverse myelitis may occur rarely following vaccination.[431] Signs and symptoms include muscle weakness, localised or radiating back pain, bladder and bowel symptoms, and changes in sensation. Evidence suggests a possible association between transverse myelitis and the AstraZeneca vaccine.[408] Cases have also been reported with mRNA vaccines, albeit more rarely.[432]

    • Estimates of incidence vary. In the UK, 122 cases of transverse myelitis have been reported with the AstraZeneca vaccine, 37 cases with the Pfizer/BioNTech vaccine, and 4 cases with the Moderna vaccine (as of 20 April 2022).[408]

    • People who have an episode of transverse myelitis following the first dose of the AstraZeneca vaccine should not receive a second dose of this vaccine.[408]

  • Other adverse events and safety signals

    • See table below for a complete list of adverse events included in the manufacturer’s prescribing information. Other reported adverse events (e.g., case reports) and safety signals are detailed below; however, a causal link may not have been confirmed, and this list is not exhaustive.

    • Cardiovascular/pulmonary: myocardial infarction, Takotsubo cardiomyopathy, isolated tachycardia.[433] An epidemiological study suggests a slightly increased risk for myocardial infarction and pulmonary embolism after adenovirus vector vaccines, and the European Medicines Agency is currently assessing this risk.[434][435]

    • Dermatological: Stevens-Johnson syndrome, cutaneous vasculitis, erythematous and indurated skin reactions.[436][437][438]

    • Endocrine: Graves' disease, subacute thyroiditis, menstrual disorders.[408][439][440][441]

    • Gastrointestinal: acute necrotising pancreatitis, autoimmune hepatitis (although the European Medicines Agency has ruled out a causal link at this stage).[442][443][444][445][446]

    • Haematological: acquired haemophilia A.[447]

    • Neurological: varicella zoster virus reactivation, demyelinating diseases, neuropathy, haemorrhagic stroke, myasthenic disorders, encephalopathy/encephalitis, acute disseminated encephalomyelitis, acute demyelinating polyneuropathy, new-onset multiple sclerosis, neuromyelitis optica spectrum disorder, sensorineural hearing loss.[415][448][449][450][451][452][453][454]

    • Renal: minimal change disease, IgA nephropathy, vasculitis, membranous nephropathy, scleroderma renal crisis.[455]

    • Rheumatological: rheumatoid arthritis, systemic lupus erythematosus, inflammatory myositis, adult-onset Still's disease.[443][456][457]

    • Fatal adverse events have been reported rarely post vaccination, and have been confirmed in postmortem studies.[458]

  • Report all suspected adverse events after vaccination via your local reporting system. This is mandatory in some countries. Surveillance of adverse events is extremely important, and may reveal additional, less frequent serious adverse events not detected in clinical trials. The mRNA vaccines have not been authorised for use in humans previously, so there is no long-term safety and efficacy data available for these types of vaccines.

Common

Uncommon

Comirnaty® (tozinameran)

Pfizer/BioNTech

headache; arthralgia; myalgia; injection-site reactions; fatigue; fever; chills; nausea; vomiting; diarrhoea; syncope (after administration)

lymphadenopathy; malaise; anaphylaxis; hypersensitivity; acute peripheral facial paralysis; insomnia; pain/swelling in extremity (vaccinated limb); face swelling (dermatological fillers present); myocarditis/pericarditis; decreased appetite; lethargy; hyperhidrosis; night sweats; asthenia; erythema multiforme

Spikevax® (elasomeran)

Moderna

headache; arthralgia; myalgia; injection-site reactions (may be delayed); fatigue; fever; chills; nausea; vomiting; diarrhoea; rash; lymphadenopathy; syncope (after administration)

abdominal pain; acute peripheral facial paralysis; hypoaesthesia; paraesthesia; anaphylaxis; hypersensitivity; face swelling (dermatological fillers present); myocarditis/pericarditis; dizziness; erythema multiforme

Vaxzevria®

AstraZeneca

headache; arthralgia; myalgia; injection-site reactions; pain in extremity (vaccinated limb); fatigue; malaise; fever; chills; asthenia; nausea; vomiting; diarrhoea; influenza-like illness; syncope (after administration)

lymphadenopathy; dizziness; somnolence; decreased appetite; lethargy; abdominal pain; migraine; hyperhidrosis; pruritus; rash; urticaria; angioedema; anaphylaxis; hypersensitivity; neuroinflammatory disorders; facial paralysis; muscle spasms; thrombosis with thrombocytopenia; cerebrovascular venous sinus thrombosis; immune thrombocytopenia; thrombocytopenia; capillary leak syndrome; Guillain-Barre syndrome; transverse myelitis

Nuvaxovid®

Novavax

headache; nausea; vomiting; myalgia; arthralgia; injection-site reactions; fatigue; malaise; fever; chills; pain in extremity (vaccinated limb); syncope (after administration)

lymphadenopathy; hypertension; rash; erythema; pruritus; urticaria

Ad26.COV2-S

Janssen

headache; nausea; myalgia; fatigue; injection-site reactions; cough; arthralgia; fever; chills; syncope (after administration)

tremor; dizziness; paraesthesia; sneezing; oropharyngeal pain; diarrhoea; vomiting; rash; hyperhidrosis; muscular weakness; pain in extremity (vaccinated limb); back pain; asthenia; malaise; lymphadenopathy; hypersensitivity; urticaria; Guillain-Barre syndrome; tinnitus; venous thromboembolism; thrombosis with thrombocytopenia; immune thrombocytopenia; anaphylaxis; capillary leak syndrome; small vessel vasculitis

VLA2001

Valneva

injection-site reactions; fatigue; headache; myalgia; nausea; vomiting; fever; syncope (after administration)

lymphadenopathy; dizziness; lethargy; hypoaesthesia; paraesthesia; dysgeusia; diarrhoea; abdominal pain; hyperhidrosis; rash; urticaria; pain in extremity; muscle spasms; arthralgia

Adverse effects associated with vaccines authorised in the UK. Information is taken from the UK Summary of Product Characteristics. Last updated: 12 May 2022

Vaccines: special patient populations

  • Pregnancy

    • The WHO recommends offering vaccination to all in pregnant women. The WHO does not recommend pregnancy testing prior to vaccination, or delaying pregnancy or terminating a pregnancy because of vaccination.[338][339][340][341]

    • In the UK, the JCVI and the Royal College of Obstetricians and Gynaecologists recommend that vaccination should be offered to pregnant women at the same time as the rest of the population, based on age and clinical risk (preferably with an mRNA vaccine).[459][460]

    • In the US, the Centers for Disease Control and Prevention and the American College of Obstetricians and Gynecologists recommend that all pregnant women, or women who are thinking about or trying to become pregnant, should be vaccinated.[364][461]

    • There are limited safety and efficacy data available in pregnant women.[462] Observational studies have not identified any safety signals as yet.[463][464][465][466][467][468] However, these data have limitations, and continued monitoring is needed to further assess the risk.

  • Breastfeeding

    • The WHO recommends offering vaccination to all breastfeeding women. The WHO does not recommend discontinuing breastfeeding because of vaccination.[338][339][340][341]

    • In the UK, the JCVI and the Royal College of Obstetricians and Gynaecologists recommend that vaccination should be offered to breastfeeding women and there is no need to stop breastfeeding.[459][460]

    • In the US, the Centers for Disease Control and Prevention and the American College of Obstetricians and Gynecologists recommend that all breastfeeding women should be vaccinated.[364][461]

    • There are limited safety and efficacy data available in breastfeeding women. Studies have found robust secretion of SARS-CoV-2 specific immunoglobulin A (IgA) and IgG antibodies in breast milk after vaccination.[469] However, it is unclear how long antibodies persist in the breast milk after vaccination, and their impact on the prevention of infection in infants is also unclear. Vaccine-associated mRNA was not detected in 13 milk samples collected 4 to 48 hours after vaccination from 7 breastfeeding individuals.[470] However, further research is required.

  • Children and adolescents (12 to 17 years of age)

    • The WHO recommends that children and adolescents aged 12 to 17 years of age with comorbidities that put them at higher risk of serious disease should be offered vaccination with the Pfizer/BioNTech or Moderna vaccines. The WHO recommends that countries consider vaccination in this age group only when high vaccine coverage (primary series and boosters) has been achieved in the higher priority-use groups.[338][339]

    • The Pfizer/BioNTech and Moderna vaccines have been authorised for use in children aged ≥12 years and adolescents in some countries. Authorisation was based on an ongoing randomised, placebo-controlled clinical trial of over 2000 participants that reported 100% efficacy from 7 days after the second dose.[471] Due to the limited number of children included in the study, the trial could not have detected rare adverse effects such as myocarditis. However, safety monitoring of VAERS noted over 9000 reports of adverse events post-vaccination in adolescents aged 12 to 17 years (as of 16 July 2021), 9.3% of which were for serious adverse events including myocarditis (4.3%).[472]

    • The Pfizer/BioNTech vaccine may be preferred over the Moderna vaccine in this age group due to a lower reported rate of myocarditis/pericarditis.[367] The US Food and Drug Administration has put an application for the authorisation of the Moderna vaccine in this age group on hold while it investigates the risk.[473]

    • In the UK, the JCVI recommends that all children aged 12 to 15 years should be offered their second dose of the Pfizer/BioNTech vaccine at a minimum of 12 weeks after the first dose. The interval may be reduced to at least 8 weeks if the emerging epidemiological data support this. Those aged 16 to 17 years may also be offered their second dose with an interval of at least 8 weeks.[372]

    • In the US, the the Centers for Disease Control and Prevention recommends vaccination with the Pfizer/BioNTech vaccine in all children and adolescents aged ≥12 years (primary vaccination series and booster doses). The Moderna and Janssen vaccines are not currently recommended in this age group.[364]

    • Available evidence suggests that the safety and efficacy of vaccines are acceptable in this age group. Older children and adolescents were at significantly increased risk of adverse reactions after vaccination compared with younger children. There is a need for additional multicentre, large-sample studies and long-term follow-up data.[474]

    • Consult your local guidance as recommendations on vaccinating children and adolescents vary.

  • Children (5 to 11 years of age)

    • The WHO recommends that children aged 5 to 11 years of age with comorbidities that put them at higher risk of serious disease should be offered vaccination with the Pfizer/BioNTech vaccine. The WHO recommends that countries consider vaccination in this age group only when high vaccine coverage (primary series and boosters) has been achieved in the higher priority-use groups.[338]

    • The Pfizer/BioNTech vaccine has been authorised for use in children aged 5 to 11 years in some countries. Authorisation was based on an ongoing randomised placebo-controlled clinical trial of approximately 4700 children 5 to 11 years of age that reported 90.7% efficacy from 7 days after the second dose. Safety analysis was based on only 1444 participants.[475] Due to the limited number of children included in the study, the trial could not have detected rare adverse effects such as myocarditis. However, preliminary real world data has not picked up an increased risk of myocarditis in this age group as yet.[476]

    • In the UK, the JCVI recommends that children aged 5 to 11 years who are in a clinical risk group, or who are a household contact of someone (of any age) who is immunosuppressed, should be offered a primary course of the Pfizer/BioNTech vaccine.[373] Although this age group is generally at very low risk of serious illness from the virus, the committee has also advised a non-urgent offer of vaccination to all children aged 5 to 11 years of age.[477] The UK’s Medicines and Healthcare products Regulatory Agency has approved the Moderna vaccine for children aged 6 to 11 years.[478]

    • In the US, the Centers for Disease Control and Prevention recommends a primary course of vaccination with the Pfizer/BioNTech vaccine in all children ages 5 to 11 years (primary vaccination series only; booster doses are not currently recommended in this age group). The Moderna and Janssen vaccines are not currently recommended in this age group.[364]

    • Use caution when administering the vaccine to this age group. A lower dose of the Pfizer/BioNTech vaccine is recommended, and the most common adverse events in this age group were related to administration errors.[476] Vaccine vials may have different coloured caps to help prevent dose administration errors.

    • Available evidence suggests that the safety and efficacy of vaccines are acceptable in this age group. There is a need for additional multicenter, large-sample studies and long-term follow-up data.[474]

    • Consult your local guidance as recommendations on vaccinating children vary.

  • Current or previous SARS-CoV-2 infection

    • Delayed vaccination is recommended in people with current acute COVID-19 or any other acute febrile illness (until they have recovered from the acute illness and are afebrile and the criteria for discontinuation of isolation have been met), and people who previously received passive antibody therapy for COVID-19 (for at least 90 days). Delayed vaccination may also be considered in people who have had confirmed SARS-CoV-2 infection in the preceding 3 to 6 months (until near the end of this period).[338][339][340][341]

    • Emerging data indicate that symptomatic reinfection may occur sooner in settings where variants of concern are circulating. In these settings, earlier immunisation after infection may be advisable (e.g., within 90 days following natural infection).[338]

    • Emerging evidence suggests that one dose of the vaccine may be sufficient for people who have already been infected with SARS-CoV-2.[479][480][481]

    • A higher rate of adverse effects has been reported after the first dose of the vaccine in people with a history of SARS-CoV-2 infection compared with participants who had not previously been infected, but not after the second dose.[482]

  • Immunocompromised

    • Seroconversion rates were significantly lower in immunocompromised people, especially solid organ transplant recipients, but increased after the second dose. However, seroconversion remained severely reduced in solid organ transplant recipients even after a second dose compared with the general population.[483] Approximately 20% to 40% of solid organ transplant recipients did not mount an antibody response despite receiving multiple doses of mRNA vaccines.[484]

  • Autoimmune disease

    • Data suggests that vaccine efficacy may be lower in patients with autoimmune disease.[485][486][487] It is uncertain whether vaccines may cause an exacerbation of pre-existing autoimmune diseases; however, there are case reports of new autoimmune conditions or flares of existing autoimmune conditions post vaccination.[488][489][490][491] Further research is needed to understand vaccine efficacy among this group.

  • Malignancy

    • Data suggests that vaccine efficacy may be lower in cancer patients compared with the general population. Antibody response was lower in haematological malignancies compared with solid tumours. Antibody response was also lower for allogeneic and autologous haematopoietic stem cell transplant recipients, and those receiving active treatment. The response varied depending on the treatment; lower responses were reported for anti-CD20 therapies, Bruton kinase inhibitors, venetoclax, ruxolitinib, and chimeric antigen receptor T-cell therapy.[492] Further research is needed to understand vaccine efficacy among this group.

Vaccines: efficacy

  • Initial authorisation of vaccines was based on interim analyses of ongoing phase 3 clinical trials with a median follow-up of 2 months. Overall initial reported vaccine efficacy for preventing symptomatic infection was reported as 95% (Pfizer/BioNTech), 94.1% (Moderna), 74% (AstraZeneca), and 66.9% (Janssen).[493][494][495][496]

  • Observational evidence from the initial global vaccine rollout suggested real-world efficacy in reducing the rate of symptomatic or asymptomatic infection, disease severity, hospitalisation, death, and possibly even reinfection. However, evidence indicates a minimal to modest reduction of vaccine protection against severe disease over the 6 months after the primary series, while waning efficacy against all clinical disease and infection is more pronounced. Vaccine efficacy against severe disease decreased by about 8% over a 6-month period in all age groups (10% in those aged >50 years), and vaccine efficacy against symptomatic disease decreased by 32% in those aged >50 years.[370]

  • Vaccine efficacy varies depending on the SARS-CoV-2 variant. Efficacy is highest for the Alpha variant, with lower efficacy reported for Beta and Gamma variants.[497] There is a lack of evidence for the Delta variant; however, vaccine efficacy (in terms of testing positive and onwards transmission) for the Delta variant appears to be reduced relative to other variants.[498][499][500] See the Classification section for evolving information on vaccine efficacy against the Omicron variant.

  • Observational studies suggest that people who receive at least one dose of the Pfizer/BioNTech vaccine after prior SARS-CoV-2 infection may have a decreased risk of recurrent/breakthrough infection compared with those who remain unvaccinated; however, these studies have many limitations.[501][502][503]

  • Previous trials of coronavirus vaccines identified cellular immunopathology and antibody-dependent enhancement as potential safety issues.[504][505]

    • Available data do not indicate a risk of vaccine-enhanced disease with the mRNA vaccines; however, data are limited and the risk over time, potentially associated with waning immunity, remains unknown and needs to be evaluated further.[493][494] The possibility of antibody-dependent enhancement in people receiving vaccines based on the original virus strain spike sequence who are then exposed to the Delta variant has not been studied.[506]

Monoclonal antibodies: pre-exposure prophylaxis

  • Tixagevimab/cilgavimab is authorised in some countries for pre-exposure prophylaxis.

    • Tixagevimab/cilgavimab is a long-acting, neutralising monoclonal antibody combination with activity against SARS-CoV-2. It is designed to attach to the spike protein of the virus at two different sites.

    • It is authorised for use in the US, the UK, and Europe.[507][508][509]

  • Guideline recommendations for the use of tixagevimab/cilgavimab vary. Consult your local guidance.

    • In the US, the National Institutes of Health guidelines panel recommends tixagevimab/cilgavimab for pre-exposure prophylaxis in children aged ≥12 years (weighing ≥40 kg) and adults who do not have SARS-CoV-2 infection, who have not been recently exposed to an individual with SARS-CoV-2 infection, AND who are moderately to severely immunocompromised and may have an inadequate immune response to vaccination, or are not able to be fully vaccinated with any available COVID-19 vaccines due to a documented history of severe reactions. This included people with advanced or untreated HIV infection.[19]

    • The Infectious Diseases Society of America supports the use of tixagevimab/cilgavimab for pre-exposure prophylaxis.[510]

  • Consult your local drug formulary for information about contraindications, cautions, adverse effects, and drug interactions before prescribing this treatment.

    • Tixagevimab/cilgavimab is given as a single dose administered as two separate consecutive intramuscular injections.

    • Serious cardiac adverse events were reported infrequently in the clinical trial; however, it is unknown whether these events were caused by the drug.

  • Circulating SARS-CoV-2 variants may be associated with resistance to monoclonal antibodies.

    • In vitro data show that the Omicron BA.1 and BA.1.1 subvariants have decreased susceptibility to tixagevimab/cilgavimab.[19] However, according to the manufacturer, in vivo data suggests that tixagevimab/cilgavimab retains neutralising activity against Omicron variants (including the BA.2 subvariant).[511]

    • Dose recommendations may depend on the local circulating variant and whether the patient has had the treatment previously.

    • Consult local guidance for details regarding specific variants and resistance.

  • Evidence is limited.

    • In an ongoing multicentre, double-blind, parallel-group, randomised, placebo-controlled trial, tixagevimab/cilgavimab reduced the risk of developing symptomatic disease by 76.7% (relative risk reduction) compared with placebo at the primary analysis (median 83 days after administration), with an 82.8% relative risk reduction reported at the median 6-month follow-up. All cases of severe or critical disease were reported in the placebo group. The most common adverse event was injection-site reactions.[512]

    • A small cohort study found that pre-exposure administration of tixagevimab/cilgavimab was associated with a lower risk of infection in severely immunocompromised patients with immune-mediated inflammatory diseases who were fully vaccinated. However, due to the limitations of the study, these results should be interpreted with caution.[513]

Infection prevention and control for healthcare professionals

  • Consult local infection prevention and control protocols; only basic principles from the World Health Organization (WHO) guidelines are detailed here.[514][515]

  • Screen all people, including patients, visitors, and others entering the facility, for COVID-19 at the first point of contact with the health facility to allow for early recognition.

  • Immediately isolate all suspected or confirmed cases in a well-ventilated area that is separate from other patients. Place patients in adequately ventilated single rooms if possible. When single rooms are not available, place all cases together in the same adequately ventilated room and ensure there is at least 1 metre (3 feet) between patients.

  • Implement standard precautions at all times:

    • Practice hand and respiratory hygiene

    • Give patients a medical mask to wear

    • Wear appropriate personal protective equipment

    • Practice safe waste management and environmental cleaning.

  • Implement additional contact and droplet precautions before entering a room where suspected or confirmed cases are admitted.

    • A respirator or medical mask should be worn along with other personal protective equipment (i.e., gown, gloves, eye protection) before entering a room with a suspected or confirmed case.

    • A respirator should be worn in the following situations: in care settings where ventilation is known to be poor or cannot be assessed, or the ventilation system is not properly maintained; based on the worker’s values and preferences and on their perception of what offers the highest protection possible to prevent infection.

    • Appropriate mask fitting should always be ensured, as should compliance with appropriate use of personal protective equipment and other precautions.

    • Universal masking is strongly recommended in health facilities in areas of known or suspected community or cluster transmission.

  • Implement airborne precautions when performing aerosol-generating procedures, including placing patients in a negative pressure room and wearing a particulate respirator.

    • A respirator should always be worn along with other personal protective equipment while performing aerosol-generating procedures, and in settings where these procedures are regularly performed on patients with suspected or confirmed disease (e.g., intensive care units, emergency departments).

    • Some countries and organisations recommend airborne precautions for any situation involving the care of a COVID-19 patient.

  • All specimens collected for laboratory investigations should be regarded as potentially infectious.

  • Appropriate personal protective equipment gives healthcare workers a high level of protection.

    • A cross-sectional study of 420 healthcare workers deployed to Wuhan with appropriate personal protective equipment tested negative for SARS-CoV-2 on molecular and serological testing when they returned home, despite all participants having direct contact with COVID-19 patients and performing at least one aerosol-generating procedure.[516]

    • Standard surgical masks are as effective as respirator masks for preventing infection of healthcare workers in outbreaks of viral respiratory illnesses such as influenza, but it is unknown whether this applies to COVID-19.[517]

  • Avoid in-person assessment of patients with suspected COVID-19 in primary care when possible to avoid infection. Most patients can be managed remotely by telephone or video consultations.[518]

  • Detailed infection prevention and control guidance is available:

Infection prevention and control for the general public

  • Public health recommendations vary between countries and you should consult your local guidance.

    • It is generally recommended that people stay at least 1 to 2 metres (3-6 feet) away from others (recommendations vary between countries), wash their hands often with soap and water (or hand sanitiser that contains at least 60% alcohol), cover coughs and sneezes, wear a mask (see Face masks below), avoid crowds and poorly ventilated spaces, clean and disinfect high touch surfaces, monitor their health and self-isolate or seek medical attention if necessary, and get vaccinated.[519][520]

    • WHO: advice for the public – coronavirus disease (COVID-19) Opens in new window

  • Countries may sometimes implement non-pharmaceutical interventions in order to reduce and delay viral transmission (e.g., social distancing, city lockdowns, stay-at-home orders, curfews, non-essential business closures, bans on gatherings, school and university closures, remote working, quarantine of exposed people).

    • Implementing any non-pharmaceutical interventions was associated with a significant reduction in case growth when comparing countries with more restrictive non-pharmaceutical interventions to countries with less restrictive non-pharmaceutical interventions. However, there was no clear, significant beneficial effect of more restrictive non-pharmaceutical interventions compared with less restrictive non-pharmaceutical interventions in any of the countries studied.[521]

    • Negative consequences of community-based mass quarantine include psychological distress, food insecurity, economic challenges, diminished healthcare access, heightened communication inequalities, alternative delivery of education, and gender-based violence.[522]

  • Some countries have published guidance to support the next stage of the pandemic, living with COVID-19. This new phase focuses on protecting those who are most at risk from the virus. Consult your local guidance.

  • The following guidance has been published in the UK:

Face masks

  • Public health recommendations on wearing face masks vary between countries and you should consult your local guidance. Many countries have ended mask mandates, except in certain high-risk situations.

  • The WHO recommends wearing a mask, regardless of vaccination status or history of prior infection, in settings where there is community or cluster transmission when interacting with non-household members in the following circumstances:[515]

    • Indoor settings where ventilation is poor or cannot be assessed, regardless of whether physical distancing of at least 1 metre (3 feet) can be maintained

    • Indoor settings with adequate ventilation if physical distancing cannot be maintained

    • Outdoor settings if physical distancing cannot be maintained

    • For people who are at higher risk of severe complications from infection, if physical distancing cannot be maintained in any setting.

  • Masks are not recommended:

    • During vigorous-intensity physical activity

    • In children aged <5 years for source control (a risk-based approach should be applied to children aged 6-11 years)

    • In children with severe cognitive or respiratory impairments, developmental disorders, disabilities, or other specific health conditions who experience difficulties wearing a mask or have health conditions that interfere with mask-wearing.

  • There is no high-quality or direct scientific evidence to support the widespread use of masks by healthy people in the community setting. Data on effectiveness is based on limited and inconsistent observational and epidemiological studies.

    • The only randomised controlled trial to investigate the efficacy of masks in the community found that the recommendation to wear surgical masks when outside the home did not reduce infection compared with a no mask recommendation. However, the study did not assess whether masks could decrease disease transmission from mask wearers to others (source control).[523] Evidence from randomised controlled trials for other respiratory viral illnesses shows no significant benefit of masks in limiting transmission but is of poor-quality and not SARS-CoV-2-specific.[524]

    • A Cochrane review found that wearing a mask may make little to no difference in how many people caught influenza-like illnesses. However, this was based on low-certainty evidence, and does not include results of studies from the current pandemic.[525]

    • A living rapid review found that the evidence for mask effectiveness for respiratory tract infection prevention is stronger in healthcare settings compared with community settings; however, direct evidence on comparative effectiveness in SARS-CoV-2 infection is insufficient. The strength of evidence for any mask use versus non-use in community settings is low-moderate.[526][527]

    • Cloth masks have limited efficacy in preventing viral transmission compared with medical-grade masks and the efficacy is dependent on numerous factors (e.g., material type, number of layers, fitting, moisture level), and may result in increased risk of infection.[528][529]

  • There are harms and disadvantages of wearing masks including headache, breathing difficulties, facial skin lesions, irritant dermatitis, worsening acne, difficulty wearing masks by certain members of the population (e.g., children, people with learning disabilities, mental illness or cognitive impairment, asthma, chronic respiratory or breathing problems, facial trauma or recent oral maxillofacial surgery, living in hot and humid environments), psychological issues, difficulty communicating, poor compliance, waste disposal issues, and increased viral load. There are insufficient data to quantify all of the adverse effects that might reduce the acceptability, adherence, and effectiveness of face masks.[515][530][531]

Travel-related control measures

  • Many countries have implemented measures including complete or partial closure of borders, entry or exit screening, and/or quarantine of travellers. Consult your local guidance.

    • Low- to very low-certainty evidence suggests that travel-related control measures may help to limit the spread of infection across national borders. Cross-border travel restrictions are likely to be more effective than entry and exit screening, and screening is likely to be more effective in combination with other measures (e.g., quarantine, observation).[532]

    • Low-certainty evidence suggests that screening at travel hubs may slightly slow the importation of infected cases; however, the evidence base comes from two mathematical model studies and is limited by their assumptions. Evidence suggests that one-time screening in apparently healthy people may miss between 40% and 100% of people who are infected, although the certainty of this ranges from very low to moderate. In very low‐prevalence settings, screening for symptoms or temperature may result in few false negatives and many true negatives, despite low overall accuracy. Repeated screenings may result in more cases being identified eventually and reduced harm from false reassurance.[533]

    • A Cochrane review found quarantine to be important in reducing the number of people infected and deaths, especially when started earlier and when used in combination with other prevention and control measures. However, the current evidence is limited because most studies are based on mathematical modelling studies that make assumptions on important model parameters.[534]

  • The psychosocial effects of enforced quarantine may have long-lasting repercussions.[535][536]

  • UK Health Security Agency: travel abroad - step by step Opens in new window

Lifestyle modifications

  • Lifestyle modifications (e.g., smoking cessation, weight loss) may help to reduce the risk of infection, and may be a useful adjunct to other interventions.[537]

  • The WHO recommends that tobacco users stop using tobacco given the well-established harms associated with tobacco use and second-hand smoke exposure.[211] The UK Health Security Agency also recommends stopping smoking.

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