Epidemiology

Over 238.5 million cases have been reported globally, with approximately 4.8 million deaths according to the World Health Organization. The US has the highest number of reported infections and deaths in the world. India, Brazil, the UK, and Russia have the highest number of infections after the US. Brazil, India, Mexico, and Russia have the highest number of deaths after the US.

WHO: coronavirus disease (COVID-19) dashboard external link opens in a new window

com.bmj.content.model.Caption@3bd99983[Figure caption and citation for the preceding image starts]: Number of COVID-19 cases reported weekly by WHO Region, and global deaths, as of 10 October 2021World Health Organization [Citation ends].

Current detailed data for the US situation is available.

Adults

  • In China, 87% of confirmed cases were ages 30 to 79 years and 3% were ages 80 years or older in the first wave of the pandemic. Approximately 51% of patients were male.[9] 

  • In the UK, the median age of patients was 73 years and males accounted for 60% of admissions in a prospective observational cohort study of more than 20,000 hospitalized patients in the first wave.[10]

  • In the US, older patients (ages ≥65 years) accounted for 31% of all cases, 45% of hospitalizations, 53% of intensive care unit admissions, and 80% of deaths in the first wave, with the highest incidence of severe outcomes in patients ages ≥85 years.[11]

Adolescents

  • Adolescents appear to have similar susceptibility to infection as adults.[12] However, evidence is conflicting and the detailed relationship between age and susceptibility to infection requires further investigation.[13]

  • In the US, hospitalizations in adolescents peaked at 2.1 per 100,000 in early January 2021, declined to 0.6 per 100,000 in March, and rose to 1.3 per 100,000 in April. Among hospitalized adolescents, approximately one third required admission to the intensive care unit and 5% required mechanical ventilation. This data was based on 204 adolescents who were likely hospitalized primarily for COVID-19 during January 1 to March 31 2021.[14] The cumulative number of hospitalizations in the 5- to 17-year-old age bracket from March 2020 to June 2021 was 1909 cases.[15]

Children

  • Evidence suggests that children have a lower susceptibility to infection compared with adults.[12] However, evidence is conflicting and the detailed relationship between age and susceptibility to infection requires further investigation.[13] Emerging data suggests variants may spread more effectively and rapidly among young children, although hospitalization rates decreased.[16]

  • Most cases in children are from familial clusters, or children who have a history of close contact with an infected patient. It is rare for children to be the index case in household transmission clusters.[17] Unlike adults, children do not seem to be at higher risk for severe illness based on age or sex.[18]

  • In the UK, a prospective observational cohort study found that children and young adults represented 0.9% of all hospitalized patients at the time. The median age of children admitted to hospital was 4.6 years, 56% were male, 35% were under 12 months of age, and 42% had at least one comorbidity. In terms of ethnicity, 57% were White, 12% were South Asian, and 10% were Black. Age under 1 month, age 10 to 14 years, and Black race were risk factors for admission to critical care.[19]

  • In the US, a retrospective cohort study of over 135,000 children found that the mean age of infected children was 8.8 years, and 53% were male. In terms of ethnicity, 59% were White, 15% were Black, 11% were Hispanic, and 3% were Asian. Only 4% of children tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in this population, and clinical manifestations were typically mild.[20]

  • Globally, the case fatality rate in children appears to be higher in low- and middle-income countries compared with high-income countries.[21]

Pregnant women

  • The overall prevalence in pregnant and recently pregnant women attending or admitted to hospital for any reason has been estimated to be 10%; however, the rate varies across studies and countries.[22][23] A meta-analysis of over 2500 pregnant women with confirmed disease found that 73.9% of women were in the third trimester; 50.8% were from Black, Asian, or minority ethnic groups; 38.2% were obese; and 32.5% had chronic comorbidities.[24]

  • In the UK, the estimated incidence of admission to hospital with confirmed infection in pregnancy is 4.9 per 1000 maternities. Most women were in the second or third trimester. Of these patients, 41% were ages 35 years or older, 56% were from Black or other ethnic minority groups, 69% were overweight or obese, and 34% had preexisting comorbidities.[25]

  • In the US, over 125,000 cases have been reported in pregnant women (as of 4 October 2021), with over 22,000 hospitalizations and 171 deaths.[26] According to an analysis of approximately 400,000 women ages 15 to 44 years with symptomatic disease, Hispanic and non-Hispanic Black pregnant women appear to be disproportionately affected during pregnancy.[27]

Healthcare workers

  • Approximately 14% of the cases reported to the World Health Organization are in healthcare workers (range 2% to 35%).[28]

  • The incidence of infection in healthcare workers ranged from 0% to 49.6% (by polymerase chain reaction), and the prevalence of SARS-CoV-2 seropositivity ranged from 1.6% to 31.6%. The wide ranges are likely related to differences in settings, exposures, rates of community transmission, symptom status, use of infection control measures, and other factors. There was no consistent association between sex, age, or healthcare worker role (i.e., nurse versus physician) and risk for infection or seropositivity. However, Black or Hispanic ethnicity was significantly associated with an increased risk of infection compared with White people. Working in a hospital unit with COVID-19 patients, being a frontline worker, and direct or prolonged patient contact were also associated with an increased risk for infection. The presence of immunoglobulin G antibodies was associated with a decreased risk for reinfection.[29][30]

Use of this content is subject to our disclaimer