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Age specificity of cases and attack rate of novel coronavirus disease (COVID-19)

Our take —

Age-stratified data from Japan suggest that children may be less likely to acquire COVID-19 and become cases compared to older adults (50 years and older). Still, attack rates among children indicate a risk of disease. Importantly, data do not demonstrate that children are at a lower risk of infection, and do not provide information on asymptomatic transmission which may still be ongoing despite lower disease risk. Given the recent resurgence of new cases in Japan, it would be useful to update these numbers.

Study design

Case Series

Study population and setting

This study examines the age-distribution of confirmed cases of SARS-CoV-2 between January and March 2020 in Japan. Age-specific attack rates were also calculated.

Summary of Main Findings

There were a total of 313 domestically-acquired cases emerging from 2496 suspected cases with close contacts and confirmed via RT-PCR, as of March 7, 2020 in Japan. Overall, there was a higher proportion of cases that were male (55.2%). A total of ten cases (3%) were among those 0-19 years old, while 131 cases were among those 60 years or older (42%). The attack rate for those 0-19 years old was 7.2% (95% CI: 3.0%, 14.3%) among males and 3.8% (95% CI: 0.8%, 10.6%) among females. The highest attack rate was seen among those 50-59 year old for both males (22.2%) and females (21.9%).

Study Strengths

This study provides initial descriptive data for Japan that reinforces age-related data observed in other settings.

Limitations

This is a relatively small study with limited information about the suspected index cases or testing information about contacts which prevent understanding of infection risk (versus disease).

Value added

This small study provides additional evidence that supports that children may be less likely to be diagnosed as cases, and that even given documented exposure, the risk of children acquiring the disease is low.