Vaccines are available under temporary emergency use or conditional marketing authorisations in various countries.
Immunisation programmes generally prioritise people who are at highest risk from serious disease or death (e.g., residents and staff in care homes, older people, healthcare workers, and those with underlying health conditions). However, priorities differ between countries and you should consult local guidance.
It is unknown whether vaccines prevent asymptomatic infection or transmission from individuals who are infected despite vaccination. Vaccinated people should continue to follow public health recommendations. Safety and efficacy, including duration of immunity, beyond 2 months is unknown. Advice will be updated as information on the impact of vaccination on virus transmission and indirect protection in the community is assessed.
In the US, the Centers for Disease Control and Prevention recommends that people who have been vaccinated do not need to quarantine after exposure to a person with COVID-19 provided they meet the following criteria: they have received both doses of the vaccine and at least 2 weeks have passed since the second dose; they are within 3 months of their last dose; and they have not developed symptoms of COVID-19 since their exposure.
Surveillance of adverse events is extremely important, and may reveal additional, less frequent serious adverse events not detected in clinical trials.
For example, the Pandemrix® vaccine used during the 2009-2010 swine flu pandemic was withdrawn from the market due to an association with narcolepsy.
The new authorised 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.
Laboratory-confirmed cases of COVID-19 have been reported after vaccination. Symptoms can be mistaken for vaccine-related adverse effects in the initial days after vaccination. Have a high level of suspicion of reported symptoms and avoid dismissing complaints as vaccine-related until vaccine recipients are tested and true infection is ruled out.
All suspected adverse reactions should be reported via the Yellow Card scheme in the UK. Yellow Card: coronavirus (COVID-19) external link opens in a new window
All suspected adverse reactions should be reported via the Vaccine Adverse Event Reporting System (VAERS) in the US. Vaccine Adverse Event Reporting System external link opens in a new window
Vaccine dose schedules may differ across locations.
There have been suggestions about extending the length of time between doses, reducing the number of doses, changing the dose (half-dose), or mixing and matching different COVID-19 vaccines in order to vaccinate more people. However, there is no evidence to support these strategies as yet.
The World Health Organization (WHO) recommends that countries experiencing exceptional epidemiological circumstances may consider delaying the administration of the second dose of mRNA vaccines for a short period (up to 42 days based on currently available clinical trial data) as a pragmatic approach to maximising the number of individuals benefiting from a first dose while vaccine supply continues to increase. However, evidence for this extension is not strong. Countries should ensure that any such programme adjustments to dose intervals do not affect the likelihood of receiving the second dose. The WHO does not support altering doses.
In the UK, the Joint Committee on Vaccination and Immunisation recommends that delivery of the first dose of any vaccine to as many eligible individuals as possible should be initially prioritised over delivery of a second dose. However, there is a lack of evidence to support an extended dose interval between the first and second dose, and this is outside of the manufacturer's authorised dose recommendations.
In the US, the Centers for Disease Control and Prevention recommends that the second dose of an mRNA vaccine can be scheduled for up to 6 weeks after the first dose if the recommended dosing interval cannot be met. The agency continues to emphasise that the second dose should be given as close to the recommended interval as possible, and states that the two mRNA vaccines that are available in the US may be considered interchangeable in exceptional circumstances.
Clinical trials have started in the UK to determine whether different vaccines may be used for the 2-dose regimen.
Consult local guidelines before administering vaccines. Patients must give free and voluntary informed consent prior to vaccination.
The table below compares the three main vaccines that have been authorised for use in many countries.
In addition to these, CoronaVac® and Sinopharm® (inactivated version of the severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2] virus) have been authorised in China, and Sputnik V® (an adenovirus vector vaccine) has been authorised in Russia and is 91.6% effective. A decision regarding the authorisation of the Janssen AD26.COV2.S vaccine in the US is expected on 26 February 2021.
Several other vaccine candidates are still in development including mRNA vaccines, DNA vaccines, viral vector vaccines, protein subunit vaccines, live-attenuated vaccines, inactivated virus vaccines, and intranasal delivery systems.
Pfizer/BioNTech COVID-19 vaccine
Moderna COVID-19 vaccine
AstraZeneca COVID-19 vaccine
COVID-19 mRNA vaccine BNT162b2
COVID-19 vaccine mRNA-1273
COVID-19 vaccine ChAdOx1 S recombinant
Lipid nanoparticle-formulated mRNA vaccine that encodes the SARS-CoV-2 spike protein
Adenovirus (chimpanzee) vector vaccine that carries the genetic code for the SARS-CoV-2 spike protein
55% to 80% (depending on dose interval)
UK, US, Europe, Canada
UK, US, Europe
Active immunisation of individuals ≥16 years of age
Active immunisation of individuals ≥18 years of age
0.3 mL (30 micrograms) IM; second dose at least 21 days after first dose
0.5 mL (100 micrograms) IM; second dose at least 28 days after first dose
0.5 mL IM (5 × 1010 viral particles); second dose 4-12 weeks after first dose
Hypersensitivity to active substance or any excipients; immediate allergic reaction to first dose (should not get second dose)
History of anaphylaxis/allergic reactions
Acute severe febrile illness
Bleeding disorders or anticoagulation
Pregnancy and breastfeeding
Previous treatment with COVID-19 monoclonal antibodies or plasma
History of anaphylaxis/allergic reactions
Acute severe febrile illness
Bleeding disorders or anticoagulation
Pregnancy and breastfeeding
Common: headache; arthralgia; myalgia; injection-site reactions; fatigue; fever; chills; nausea
Uncommon: lymphadenopathy; malaise; anaphylaxis; hypersensitivity; acute peripheral facial paralysis
Common: headache; arthralgia; myalgia; injection-site reactions; fatigue; fever; chills; nausea; vomiting; diarrhoea; rash; lymphadenopathy
Uncommon: malaise; acute peripheral facial paralysis; anaphylaxis; hypersensitivity; face swelling (if dermatological fillers present)
Common: headache; arthralgia; myalgia; injection-site reactions; fatigue; malaise; fever; chills; nausea; vomiting; diarrhoea; influenza-like illness
Uncommon: lymphadenopathy; dizziness; decreased appetite; abdominal pain; hyperhidrosis; pruritus; rash; neuroinflammatory disorders; anaphylaxis
Interactions with other vaccines/drugs have not been studied (WHO recommends a minimum of 14 days between COVID-19 vaccines and other vaccines)
|Information for UK healthcare professionals|
Comparison of selected authorized COVID-19 vaccines. Data is evolving; consult local drug formulary or guidelines for detailed information for your location. *See Vaccine efficacy data and Vaccine safety data sections below for detailed information. **Dose schedules may differ in some locations. Last reviewed/updated: 25 February 2021.
Vaccines and anaphylaxis or vasovagal reactions
Severe allergic reactions, including anaphylaxis, have been reported outside of clinical trials in the general population after vaccination.
In the US, monitoring by the VAERS detected 4.7 cases of anaphylaxis per million doses of the Pfizer/BioNTech vaccine, and 2.5 cases per million doses of the Moderna vaccine as of 18 January 2021.
In the UK, monitoring of the Yellow Card reporting system detected detected 168 cases of anaphylaxis with the Pfizer/BioNTech vaccine (1-2 cases per 100,000 doses), and 105 cases of anaphylaxis with the AstraZeneca vaccine as of 14 February 2021.
It has been suggested that reactions after mRNA vaccines may be due to the presence of lipid pegylated ethylene glycol (PEG), or PEG derivatives such as polysorbates.
The WHO recommends that a history of anaphylaxis to any component of the vaccine is a contraindication to vaccination for all vaccines. People with an immediate anaphylactic allergic reaction to the first dose should not receive additional doses. Administer vaccines only in settings where anaphylaxis can be treated, and observe for at least 15 minutes after vaccination.
The WHO recommends people with an immediate non-anaphylactic allergic reaction to the first dose of an mRNA vaccine (i.e. urticaria, angio-oedema, or respiratory symptoms such as cough, stridor, or wheezing without any other symptoms within 4 hours of administration) should not receive additional doses unless recommended after review by a health professional with specialist expertise. A history of any immediate allergic reaction to any other vaccine or injectable therapy is considered a precaution, but not a contraindication, to vaccination. Perform a risk assessment to determine the type and severity of reaction and the reliability of the information. These people may still be vaccinated, but the risks should be weighed against the benefits of vaccination, and the recipient should be observed for 30 minutes after vaccination in healthcare settings where anaphylaxis can be treated immediately. Anaphylactic reactions have also been reported in people without a history of severe allergic reactions. Food, insect venom, contact, or seasonal allergies, and allergic rhinitis, eczema, and asthma are not considered a precaution. There is no contraindication or precaution to vaccination for people with latex, egg, or gelatin allergies.
The UK-based Medicines and Healthcare products Regulatory Agency recommends that anyone with a previous history of allergic reactions to the ingredients of the vaccine should not receive it, but those with any other allergies such as a food allergy can have the vaccine.
Guidelines on vaccinating people with a history of allergy or anaphylaxis may differ across locations; consult local guidance.
People with a history of receiving dermal fillers may develop swelling at or near the site of filler injection (e.g., lips, face) following administration of an mRNA vaccine. This appears to be temporary and may be treated with corticosteroids.
Delayed-onset local reactions around the injection site have been reported, and are sometimes quite large.
Anxiety-related reactions, including vasovagal reactions and hyperventilation, may occur. Ensure precautions are in place to avoid injury from fainting.
Vaccines and specific patient populations
There are limited or no data available from clinical trials about the use of vaccines in specific patient populations. Despite this, the WHO recommends that the following populations may be vaccinated, depending on the vaccine used:
Older people (without an upper age limit)
People with comorbidities that have been identified as increasing the risk for severe disease
Immunocompromised people who are part of a group recommended for vaccination
People living with HIV who are part of a group recommended for vaccination
People with autoimmune conditions who have no contraindications to vaccination and who are part of a group recommended for vaccination
People with a history of Bell’s palsy who have no contraindications to vaccination
People with a history of symptomatic or asymptomatic SARS-CoV-2 infection.
Delayed vaccination is recommended in people with an acute febrile illness or current acute COVID-19 (until they are afebrile and have recovered from acute illness), and in people who previously received passive antibody therapy for COVID-19 (for at least 90 days). Delayed vaccination may be considered in people who have had confirmed SARS-CoV-2 infection in the preceding 6 months (until near the end of this period).
Antibody response to the first dose of mRNA vaccines in people with pre-existing immunity is equal to, or may exceed, titres found in those without pre-existing immunity after the second dose according to a preprint study. Also, reactogenicity is significantly higher in people who have been infected with SARS-CoV-2 in the past. Another preprint study found that one dose of the vaccine may be sufficient for people who have already been infected with SARS-CoV-2; however, further research is required.
The WHO recommends an individual risk–benefit assessment for very frail older persons with a life expectancy anticipated to be less than 3 months. The Norwegian Medicines Agency recommends conducting more thorough evaluations of very frail older patients before vaccination, after 23 patients died shortly after receiving the Pfizer/BioNTech vaccine. However, it is currently unknown whether there is a connection between these deaths and the vaccine. The agency has investigated 13 of the deaths so far and has concluded that common adverse reactions of mRNA vaccines, such as fever, nausea, and diarrhoea, may have contributed to fatal outcomes in some of the frail patients.
Vaccines and pregnant/breastfeeding women
Use caution in pregnant and breastfeeding women as there are no safety and efficacy data available. Clinical trials in pregnant women have started.
The WHO recommends not using vaccines in pregnant women, unless the benefits outweigh the potential risks (e.g., healthcare workers at high risk of exposure, women with comorbidities that place them in a high-risk group for severe disease). It recommends that women who are breastfeeding, and who are part of a group recommended for vaccination, should be offered vaccination on an equivalent basis. It does not recommend delaying pregnancy or discontinuing breastfeeding after vaccination.
Public Health England recommends that pregnant women should not routinely be vaccinated; however, vaccination may be considered when the potential benefits outweigh the potential risks for the mother and fetus. It recommends that women who are breastfeeding can receive the vaccine.
The American College of Obstetricians and Gynecologists recommends that COVID-19 vaccines should not be withheld from pregnant or breastfeeding women who meet criteria for vaccination based on recommended priority groups. Discuss the risks and benefits with the person before vaccination. Pregnant and breastfeeding women who decline vaccination should be supported in their decision.
Vaccine efficacy data
Pfizer/BioNTech COVID-19 vaccine
Efficacy is based on an interim analysis of results from a phase 3 trial of 43,448 participants (with randomisation to vaccine and placebo arms in a 1:1 ratio). The vaccine is reported to be 95% effective in preventing symptomatic COVID-19 after 2 doses compared with placebo (saline), in people aged 16 years and older. This is based on an analysis of 170 confirmed cases of COVID-19 with an onset at least 7 days after the second dose among recipients with no evidence of existing or prior SARS-CoV-2 infection (8 cases in the vaccine arm versus 162 cases in the placebo arm). Efficacy was 52% after the first dose. Among 10 cases of severe disease with onset after the first dose, 9 cases occurred in the placebo arm and 1 case occurred in the vaccine arm. This only provides preliminary evidence of vaccine-mediated protection against severe disease.
The vaccine appears to be over 90% effective in the real-world setting according to an analysis of Israel’s mass vaccination campaign. Estimated efficacy at least 7 days after the second dose was 92% for documented infection, 94% for symptomatic disease, 87% for hospitalisation, and 92% for severe disease.
Preliminary studies suggest that the vaccine may be effective against new SARS-CoV-2 variants with spike protein mutations (i.e.,B.1.1.7 and B.1.351 lineages and N501Y mutations); however, neutralisation of the B.1.351 variant may be weaker. Further research is required.
The manufacturer has started testing whether a third dose (booster) is safe and effective against currently circulating and emerging SARS-CoV-2 variants.
Moderna COVID-19 vaccine
Efficacy is based on an interim analysis of results from a phase 3 trial of 30,420 participants (with randomisation to vaccine and placebo arms in a 1:1 ratio). The vaccine is reported to be 94.1% effective in preventing symptomatic COVID-19 after 2 doses compared with placebo (saline) in people aged 18 years and older. This is based on an analysis of 196 confirmed cases of COVID-19 with an onset at least 14 days after the second dose among recipients with no evidence of existing or prior SARS-CoV-2 infection (11 cases in the vaccine arm versus 185 cases in the placebo arm). Among 30 cases of severe disease (including one fatality) with onset after the first dose, all cases occurred in the placebo arm and none in the vaccine arm.
Preliminary studies suggest that the vaccine may be effective against new SARS-CoV-2 variants with spike protein mutations (i.e., B.1.351 and B.1.1.7 lineages). Although neutralising antibody titres were lower for the B.1.351 variant compared with earlier SARS-CoV-2 variants, levels were expected to be protective, although this is yet to be confirmed. Further research is required. The manufacturer will test an additional booster dose to study the ability to further increase neutralising titres against emerging strains beyond the existing primary vaccination series. It is also advancing an emerging variant booster candidate against the B.1.351 lineage variant (known as mRNA-1273.351) into preclinical and phase 1 trials.
AstraZeneca COVID-19 vaccine
Efficacy is based on an interim analysis of pooled data from four ongoing randomised controlled clinical trials with 11,636 participants conducted in the UK, Brazil, and South Africa. The vaccine is reported to be 70.4% effective in preventing symptomatic COVID-19 after 2 doses compared with control (meningococcal vaccine or saline) in people aged 18 years and older. This is based on an analysis of 131 confirmed cases of COVID-19 with an onset at least 15 days after the second dose among recipients with no evidence of existing or prior SARS-CoV-2 infection (30 cases in the vaccine arm versus 101 cases in the placebo arm). Trial results are yet to be published. Efficacy and safety data are currently limited in people ≥65 years of age.
Vaccine efficacy appears to be higher when the interval between doses is longer. Data from a primary analysis of the clinical trials were consistent with those seen in the interim analysis, and includes results of a further month of data collection with 332 cases of symptomatic disease reported. The study found that a single standard dose provides 76% protection overall against symptomatic disease in the first 90 days after vaccination. Efficacy reached 80% after the second dose in those with a dosing interval of 12 weeks or more. However, the efficacy was only 55.1% if the two doses were given less than 6 weeks apart. The WHO recommends an interval of 8 to 12 weeks between doses.
A preprint study suggests that the vaccine may be effective against symptomatic infection caused by the B.1.1.7 SARS-CoV-2 variant. However, rollout of the vaccine in South Africa has been paused after a study found that it did not protect against mild and moderate disease caused by the B.1.351 variant.
Vaccine safety data
Pfizer/BioNTech COVID-19 vaccine
Safety is based on an interim analysis of results from a phase 3 trial of 43,448 participants. The reactogenicity subset included 8183 participants.
Local adverse reactions were more common in the vaccine group compared with placebo, with the most common reaction being injection-site pain within 7 days after injection (83% after the first dose and 78% after the second dose in younger participants; 71% after the first dose and 66% after the second dose in older participants). Less than 1% of participants reported severe pain. Local adverse reactions were similar after the first and second doses.
Systemic adverse reactions were more common in the vaccine group compared with placebo, and were reported more often by younger patients and after the second dose. The most commonly reported systemic adverse reactions after the second dose were fatigue (59% in younger participants; 51% in older participants), headache (52% in younger participants; 39% in older participants), and fever (16% in younger participants; 11% in older participants). Severe systemic events were reported in <2% of participants after either dose, except for fatigue and headache after the second dose.
Other rare adverse events included lymphadenopathy, shoulder injury (related to vaccine administration), paroxysmal ventricular arrhythmia, and right leg paraesthesia.
Moderna COVID-19 vaccine
Safety is based on an interim analysis of results from a phase 3 trial of 30,420 participants.
Solicited local and systemic adverse reactions were reported in 87.8% of participants within 7 days after the first dose in the vaccine group compared with 48% in the placebo group, and 92.2% of participants within 7 days after the second dose in the vaccine group compared with 42.8% in the placebo group. The most commonly reported solicited adverse reactions included injection-site reactions, fatigue, headache, myalgia, and arthralgia. These reactions were more commonly reported and were more severe after the second dose. Solicited adverse reactions were more common among participants aged 18 to 64 years compared with adults aged ≥65 years.
Unsolicited adverse events related to vaccination (up to 28 days after any injection) were reported in 8.2% of participants in the vaccine group compared with 4.5% in the placebo group. The incidence of severe adverse events was higher in the vaccine group compared with the placebo group (0.5% versus 0.2%). The most commonly reported unsolicited adverse events (reported in at least 1% of participants) were fatigue and headache. The relative incidence of these events was not affected by age.
Bell’s palsy occurred more commonly in the vaccine group (three cases) compared with the placebo group (one case), suggesting that it may be more than a chance event. This will require close monitoring as larger populations are vaccinated outside of clinical trials.
AstraZeneca COVID-19 vaccine
Safety is based on an interim analysis of pooled data from four ongoing randomised controlled clinical trials with 23,745 participants conducted in the UK, Brazil, and South Africa (trial results are yet to be published).
The most frequently reported adverse events were: injection-site reactions (>60%); headache, fatigue (>50%); myalgia, malaise (>40%); fever, chills (>30%); arthralgia, nausea (>20%). Adverse reactions were milder and reported less frequently after the second dose and in adults aged ≥65 years.
Vaccine trial limitations
A key limitation of the data is the short duration of safety and efficacy follow-up. Trials were not sufficiently powered to detect less common adverse events reliably, and the median follow-up time was only 2 months after the second dose. Trials do not address whether the vaccine prevents transmission or affects infectiousness, and the duration of protection is yet to be determined. There are no data on children or younger adolescents, pregnant or breastfeeding women, or immunocompromised people. There are also no data to assess efficacy in populations at high risk of severe disease, in people previously infected with SARS-CoV-2, against long-term effects of disease, or against mortality.
There are concerns that the trials were not designed to detect a reduction in any serious outcome such as hospital admissions, use of intensive care, or deaths, or whether the vaccines can interrupt transmission of the virus – two key primary end points in vaccine efficacy trials. Also, since the trials have been published, important questions about final efficacy data exclusions, as well as concerns about the use of pain and fever medications, unblinding, and primary event adjudication committees have been raised.
Planned long-term follow-up of participants is unlikely to occur in the context of trials due to the ethics of following a placebo recipient long-term without offering the vaccine. This could inadvertently threaten ongoing vaccine research that is yet to define immunological correlates of protection against COVID-19, which could vary according to the vaccine platform, individual characteristics, age groups, and population subset.
Previous trials of coronavirus vaccines identified cellular immunopathology and antibody-dependent enhancement (ADE) as potential safety issues. There are concerns over ADE of SARS-CoV-2 due to subsequent exposure to wild-type SARS-CoV-2 post vaccination and prior exposure to other coronaviruses (such as those that cause the common cold). 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.
Infection prevention and control for healthcare professionals
Always consult local infection prevention and control protocols; only basic principles are detailed here.
Immediately isolate all suspected or confirmed cases in an 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 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 cases are admitted:
Wear a medical mask, gloves, an appropriate gown, and eye/facial protection (e.g., goggles or a face shield)
Use single-use or disposable equipment.
Implement airborne precautions when performing aerosol-generating procedures, including placing patients in a negative pressure room.
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 against COVID-19. 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. 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.
Detailed infection prevention and control guidance is available:
Telehealth for primary care physicians
It is important that primary care physicians 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. Algorithms for dealing with these patients are available:
General prevention measures for the general public
Wash hands often with soap and water for at least 20 seconds or an alcohol-based hand sanitiser (that contains at least 60% alcohol), especially after being in a public place, blowing their nose, or coughing/sneezing. Avoid touching the eyes, nose, and mouth with unwashed hands
Avoid close contact with people (i.e., maintain a distance of at least 1 metre [3 feet]) including shaking hands, particularly those who are sick, have a fever, or are coughing or sneezing. Avoid going to crowded and poorly ventilated places. It is important to note that recommended distances differ between countries (for example, 2 metres is recommended in the US and UK) and you should consult local guidance. However, there is no evidence to support a distance of 2 metres
Practice respiratory hygiene (i.e., cover mouth and nose when coughing or sneezing, discard tissue immediately in a closed bin, and wash hands)
Seek medical care early if they have a fever, cough, and difficulty breathing, and share their previous travel and contact history (travellers or suspected/confirmed cases) with their healthcare provider
Stay at home and self-isolate if they are sick, even with mild symptoms, until they recover (except to get medical care)
Clean and disinfect frequently touched surfaces daily (e.g., light switches, door knobs, countertops, handles, phones).
Face masks in community settings
Recommendations on the use of face masks in community settings vary between countries. It is mandatory to wear a mask in public in certain countries or in certain situations, and masks may be worn in some countries according to local cultural habits. Consult local public health guidance for more information.
There is no high-quality or direct scientific evidence to support the widespread use of masks by healthy people in the community setting, and there are risks and benefits that must be considered. Data on effectiveness is based on limited and inconsistent observational and epidemiological studies. The first randomised controlled trial to investigate the efficacy of masks in the community (in addition to other public health measures such as social distancing) found that the recommendation to wear surgical masks when outside the home among others did not reduce incident SARS-CoV-2 infection compared with no mask recommendation. However, the study did not assess whether masks could decrease disease transmission from mask wearers to others. A Cochrane review found that wearing a mask may make little to no difference in how many people caught influenza-like illnesses; however, this is based on low-certainty evidence, and does not include results of studies from the current COVID-19 pandemic. Evidence for mask effectiveness for respiratory tract infection prevention is stronger in healthcare settings compared with community settings; direct evidence on comparative effectiveness in SARS-CoV-2 infection is insufficient. Randomised trials have not addressed the question of source control.
Despite the lack of good-quality evidence, the WHO advises that in areas of known or suspected community or cluster transmission, people should wear a non-medical mask in the following circumstances: indoor or outdoor settings where physical distancing cannot be maintained; indoor settings with inadequate ventilation, regardless of whether physical distancing can be maintained; and situations when physical distancing cannot be maintained and the person has a higher risk of severe complications (e.g., older age, underlying condition). Carers and those living with suspected or confirmed cases should wear a medical mask when in the same room, regardless of whether the case has symptoms. Children aged up to 5 years should not wear masks for source control. A risk-based approach is recommended for children aged 6 to 11 years. Special considerations are required for immunocompromised children, or children with certain diseases, developmental disorders, or disabilities. The WHO advises that people should not wear masks during vigorous-intensity physical activity. Use of a mask alone is insufficient to provide adequate protection, and they should be used in conjunction with other infection prevention and control measures such as frequent hand hygiene and social distancing.
Potential harms and disadvantages of wearing masks include: potential increased risk of self-contamination due to manipulation of face mask and touching face/eyes, or when non-medical masks are not changed when wet or soiled; headache and/or breathing difficulties; facial skin lesions, irritant dermatitis, or worsening acne; discomfort; difficulty communicating; social and psychological acceptance; false sense of security; poor compliance; waste management issues; and difficulties for patients with chronic respiratory conditions or breathing problems. Masks may also create a humid habitat where the virus can remain active and this may increase viral load in the respiratory tract; deeper breathing caused by wearing a mask may push the virus deeper into the lungs. There are insufficient data to quantify all of the adverse effects that might reduce the acceptability, adherence, and effectiveness of face masks.
Cloth masks have limited efficacy in preventing viral transmission compared with medical-grade masks. Efficacy depends on the type of material used, the number of layers, the degree of moisture in the mask, and the fitting of the mask on the face. In a study comparing the use of cloth masks to surgical masks in healthcare workers, the rates of all infection outcomes were highest in the cloth mask arm, with the rate of influenza-like illness statistically significantly higher in this group. Moisture retention, reuse of cloth masks, and poor filtration may result in increased risk of infection.
Alcohol-based hand sanitisers
The CDC has issued a warning about alcohol-based sanitisers containing methanol (which may be labelled as containing ethanol). Methanol poisoning should be considered in patients who present with relevant signs and symptoms (e.g., headache, impaired vision, nausea/vomiting, abdominal pain, loss of co-ordination, decreased level of consciousness) who report ingestion of hand sanitiser or frequent repeated topical use. Cases of permanent blindness and death have been reported.
Travel-related control measures
Many countries have implemented travel-related control measures including complete closure of borders, partial travel restrictions, entry or exit screening, and/or quarantine of travellers. Overall, low to very low 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).
Entry/exit screening: people travelling from areas with a high risk of infection may be screened using questionnaires about their travel, contact with ill persons, symptoms of infection, and/or measurement of their temperature. 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. Entry screening at three major US airports found a low yield of laboratory-diagnosed cases (one case per 85,000 travellers) between January and September 2020.
Quarantine: enforced quarantine is being used to isolate easily identifiable cohorts of people at potential risk of recent exposure. Despite limited evidence, 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. The psychosocial effects of enforced quarantine may have long-lasting repercussions.
Travellers who arrive in the UK are required to self-isolate for 10 days unless they have travelled from an exempt country. Travellers who have visited a country with a travel ban in the 10 days before arrival must self-isolate, along with their household, for 10 days from the day of departure from these countries. Public Health England: coronavirus (COVID-19) – how to self-isolate when you travel to the UK external link opens in a new window
Many countries have implemented mandatory social distancing measures in order to reduce and delay transmission (e.g., city lockdowns, stay-at-home orders, curfews, non-essential business closures, bans on gatherings, school and university closures, travel restrictions and bans, remote working, quarantine of exposed people).
Although the evidence for social distancing for COVID-19 is limited, it is emerging, and the best available evidence appears to support social distancing measures to reduce the transmission and delay spread. The timing and duration of these measures appears to be critical. When comparing countries with more restrictive non-pharmaceutical interventions (e.g., mandatory stay-at-home and business closure orders) to countries with less restrictive non-pharmaceutical interventions, implementing any non-pharmaceutical interventions was associated with a significant reduction in case growth. However, there was no clear, significant beneficial effect of more restrictive non-pharmaceutical interventions compared with less restrictive nonpharmaceutical interventions in any of the countries studied. It should be noted that the study has important limitations.
Researchers in Singapore found that social distancing measures (isolation of infected individuals and family quarantine, school closures, and workplace distancing) significantly decreased the number of infections in simulation models.
Harms must also be considered. Public health policies mostly rely on models and these models often ignore potential harms including excess death and inequalities arising from economic damage, negative health effects, and effects on vulnerable populations. 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.
Shielding extremely vulnerable people
Shielding is a measure used to protect vulnerable people (including children) who are at very high risk of severe illness from COVID-19 because they have an underlying health condition. Shielding involves minimising all interactions between those who are extremely vulnerable and other people to protect them from coming into contact with the virus.
Extremely vulnerable groups include:
Solid organ transplant recipients
People with specific cancers
People with severe respiratory conditions (e.g., cystic fibrosis, severe asthma, or severe COPD)
People with rare diseases that significantly increase the risk of infections (e.g., homozygous sickle cell disease, severe combined immunodeficiency)
People on immunosuppression therapies sufficient to significantly increase the risk of infection
People with spleen problems (e.g., prior splenectomy)
Adults with Down's syndrome
Adults on dialysis or with chronic kidney disease
Women who are pregnant with significant heart disease (congenital or acquired)
Other people who have also been classed as clinically extremely vulnerable based on clinical judgement and an assessment of their needs.
The UK government recommends that clinically extremely vulnerable people are urged to follow specific precautions based on current public health restrictions:
Consult current guidance for specific recommendations (recommendations may differ between countries).
Shielding advice for children and young adults is available. Consult current guidance for specific recommendations (recommendations may differ between countries).
Lifestyle modifications (e.g., smoking cessation, weight loss) may help to reduce the risk of COVID-19, and may be a useful adjunct to other interventions.
The WHO recommends that tobacco users stop using tobacco given the well-established harms associated with tobacco use and second-hand smoke exposure. Public Health England also recommends stopping smoking. Public Health England: COVID-19 – advice for smokers and vapers external link opens in a new window
Pre-exposure or post-exposure prophylaxis
There are no drugs recommended for pre-exposure prophylaxis or post-exposure prophylaxis, except in the context of a clinical trial. See the Emerging external link opens in a new windowsection for more information.
Some governments are discussing or implementing certifications for people who have contracted and recovered from COVID-19 based on antibody tests (sometimes called ‘immunity passports’). Possession of a passport would allow people to have a greater range of privileges (e.g., work, education, travel). However, the WHO does not support these certifications as there is currently no evidence that people who have recovered from infection and have antibodies are protected from reinfection. Other potential issues include lack of public support for these measures, potential for discrimination of groups of people, testing errors (including cross-reactivity with other human coronaviruses), access to testing, fraud, legal and ethical objections, and people getting infected intentionally in order to obtain a certification.