Children and teenagers half as likely to get infected with coronavirus than people older than 20 years: Study
An estimated 21% of those in 10 to 19 age group are likely to show symptoms compared with 69% in people aged 70 years and above
Children and teenagers are half as likely to catch Covid-19 than adults aged 20 years and older, according to researchers from the London School of Hygiene & Tropical Medicine, UK. The research team also found that even when children are infected with the new coronavirus, many have mild or subclinical symptoms. The analysis suggests that only 21% of the people in the age group of 10 to 19 years show symptoms if infected with Covid-19. This number increases to an estimated 69% for people who are 70 years or older. The Covid-19 pandemic has shown a markedly low proportion of cases among children, and the new study provides further evidence on children’s susceptibility to the disease. The evidence currently remains weak on how likely children are to transmit the virus to others. The current study also provides no information on the infectiousness of children — the level to which children can transmit the virus once infected.
The modeling study used age-specific case data from 32 settings in six countries (China, Japan, Italy, Singapore, Canada and South Korea) and data from six studies gave estimates of infection rates and symptom severity across ages.
"The distribution of confirmed Covid-19 cases has shown strong age dependence, with notably few cases in children. This could be because younger ages are less susceptible to infection and/or are less prone to showing clinical symptoms when infected. We used dynamic transmission models fitted to a range of available data on the age distribution of reported cases, and to studies that looked for infections among close contacts, to estimate the age-specific susceptibility to SARS-CoV-2 (the virus that causes Covid-19) infection and the age-specific fraction of infections that develop full clinical symptoms of Covid-19," says the team in the study published in Nature Medicine.
The findings show that those aged under 20 years are half as susceptible to infection as those over 20 and that 79% of infections are asymptomatic or paucisymptomatic (that is, subclinical) in 10 to 19-year-olds, compared with 31% in those over 70 years of age. "The age-dependent clinical fraction was markedly lower in younger age groups in all regions with 21% of infections in those aged 10 to 19 years resulting in clinical cases, which increased to 69% in adults aged over 70 years in the consensus age distribution estimated across all regions. The age-specific susceptibility profile suggested that those aged under 20 years were half as susceptible to SARS-CoV-2 infection as those aged over 20 years. Specifically, relative susceptibility to infection was 0.40 in those aged 0 to 9 years, compared with 0.88 in those aged 60 to 69 years," says the study published in Nature Medicine.
According to the team, these results have implications for the likely effectiveness of school closures in mitigating SARS-CoV-2 transmission, in that these might be less effective than for other respiratory infections. Based on their findings, the researchers say that interventions aimed at children might have a relatively small impact on reducing SARS-CoV-2 transmission, "particularly if the transmissibility of subclinical infections is low". They suggest that in countries with younger population structures, the expected per capita incidence of clinical cases would be lower than in countries with older population structures — such as many low-income countries — but it is likely that comorbidities or underlying health conditions in low-income countries will also influence disease severity. Without effective control measures, regions with relatively older populations could see disproportionally more cases of Covid-19, particularly in the later stages of an unmitigated epidemic, warn researchers.
"The role of age in transmission is critical to designing interventions aiming to decrease transmission in the population as a whole and to project the expected global burden. Our findings, together with early evidence, suggest that there is age dependence in susceptibility and the risk of clinical symptoms following infection with SARS-CoV-2. Understanding if and by how much subclinical infections contribute to transmission has implications for predicted global burden and the effectiveness of control interventions. This question must be resolved to effectively forecast and control Covid-19 epidemics," says the team.