Age-specific mortality and immunity patterns of SARS-CoV-2 infection in 45 countries

O'Driscoll, M.; Ribeiro Dos Santos, G.; Wang, L.; Cummings, D. A. T.; Azman, A. S.; Paireau, J.; Fontanet, A.; Cauchemez, S.; Salje, H.

The number of COVID-19 deaths is often used as a key indicator of SARS-CoV-2 epidemic size. 42 However, heterogeneous burdens in nursing homes and variable reporting of deaths in elderly 43 individuals can hamper comparisons of deaths and the number of infections associated with them 44 across countries. Using age-specific death data from 45 countries, we find that relative differences 45 in the number of deaths by age amongst individuals aged <65 years old are highly consistent across 46 locations. Combining these data with data from 15 seroprevalence surveys we demonstrate how 47 age-specific infection fatality ratios (IFRs) can be used to reconstruct infected population 48 proportions. We find notable heterogeneity in overall IFR estimates as suggested by individual 49 serological studies and observe that for most European countries the reported number of deaths 50 amongst [≥]65s are significantly greater than expected, consistent with high infection attack rates 51 experienced by nursing home populations in Europe. Age-specific COVID-19 death data in 52 younger individuals can provide a robust indicator of population immunity.