Age-specific rate of severe and critical SARS-CoV-2 infections estimated with multi-country seroprevalence studies

Knowing the age-specific rates at which individuals infected with SARS-CoV-2 develop severe and critical disease is essential for designing public policy, for epidemic modeling, and for individual risk evaluation. In this study, we present the first estimates of these rates using multi-country serology studies, and data on hospital admissions and mortality from early to mid-2020. We integrated data from those sources using a Bayesian model that accounts for the high heterogeneity between data sources and for the uncertainty associated to the estimates reported from each data source. Our results show that the risk of severe and critical disease increases exponentially with age, but much less steeply than the risk of fatal illness. Importantly, the estimated rate of severe disease outcome in adolescents is between one and two orders of magnitude larger than the reported rate of vaccine side-effects, showing how these estimates are relevant for health policy. Finally, we validate our results by showing that they are in close agreement with the estimates obtained from an indirect method that uses reported infection fatality rates estimates and hospital mortality data.