SARS-CoV-2 infection fatality risk in a nationwide seroepidemiological study

The magnitude of the infection fatality risk (IFR) of SARS-CoV-2 remains under debate. Because the IFR is the number of deaths divided by the number of infected, serological studies are needed to identify asymptomatic and mild cases. Also, because ascertainment of deaths attributable to COVID-19 is often incomplete, the calculation of the IFR needs to be complemented with data on excess mortality. We used data from a nation-wide seroepidemiological study and two sources of mortality information -deaths among laboratory-confirmed COVID-19 cases and excess deaths- to estimate the range of IFR, both overall and by age and sex, in Spain. The overall IFR ranged between 1.1% and 1.4% in men and 0.58% to 0.77% in women. The IFR increased sharply after age 50, ranging between 11.6% and 16.4% in men [≥]80 years and between 4.6% and 6.5% in women [≥]80 years. Our IFR estimates for SARS-CoV-2 are substantially greater than IFR estimators for seasonal influenza, justifying the implementation of special public health measures.