Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection Fatality Rate Among Elderly Danes: A Cross-sectional Study on Retired Blood Donors
Ole Birger Pedersen, Janna Nissen, Khoa Manh Dinh, Michael Schwinn, Kathrine Agergård Kaspersen, Jens Kjærgaard Boldsen, Maria Didriksen, Joseph Dowsett, Erik Sørensen, Lise Wegner Thørner, Margit Anita Hørup Larsen, Birgitte Grum-Schwensen, Susanne Gjørup Sækmose, Isabella Worlewenut Paulsen, Nanna Lond Skov Frisk, Thorsten Brodersen, Lasse S Vestergaard, Klaus Rostgaard, Kåre Mølbak, Robert Skov, Christian Erikstrup, Henrik Ullum, Henrik Hjalgrim
Abstract
BACKGROUND: Although the vast majority of individuals succumbing to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are elderly, infection fatality rate (IFR) estimates for the age group ≥70 years are still scarce. To this end, we assessed SARS-CoV-2 seroprevalence among retired blood donors and combined it with national coronavirus disease 2019 (COVID-19) survey data to provide reliable population-based IFR estimates for this age group. METHODS: We identified 60 926 retired blood donors aged ≥70 years in the rosters of 3 regionwide Danish blood banks and invited them to fill in a questionnaire on COVID-19-related symptoms and behaviors. Among 24 861 (40.8%) responders, we invited a random sample of 3200 individuals for blood testing. Overall, 1201 (37.5%) individuals were tested for SARS-CoV-2 antibodies (Wantai) and compared with 1110 active blood donors aged 17-69 years. Seroprevalence 95% confidence intervals (CIs) were adjusted for assay sensitivity and specificity. RESULTS: Among retired (aged ≥70 years) and active (aged 17-69 years) blood donors, adjusted seroprevalences were 1.4% (95% CI, .3-2.5%) and 2.5% (95% CI, 1.3-3.8%), respectively. Using available population data on COVID-19-related fatalities, IFRs for patients aged ≥70 years and for 17-69 years were estimated at 5.4% (95% CI, 2.7-6.4%) and .083% (95% CI, .054-.18%), respectively. Only 52.4% of SARS-CoV-2-seropositive retired blood donors reported having been sick since the start of the pandemic. CONCLUSIONS: COVID-19 IFR in the age group >69 years is estimated to be 65 times the IFR for people aged 18-69 years.