SARS-CoV-2 infection fatality rate among elderly retired Danish blood donors - A cross-sectional study

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 Sækmose, Isabella Worlewenut Paulsen, Nanna Lond Skov Frisk, Thorsten Brodersen, Lasse Skafte Vestergaard, Klaus Rostgaard, Kåre Mølbak, Robert Leo SkovChristian Erikstrup, Henrik Ullum, Henrik Hjalgrim

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Abstrakt

BACKGROUND: Despite 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 older are still scarce. To this end we assessed SARS-CoV-2 seroprevalence among retired blood donors and combined it with national COVID-19 survey data to provide reliable population-based IFR estimates for this age group.

METHODS: We identified 60,926 retired blood donors age 70 years or older in the rosters of three region-wide Danish blood banks and invited them to fill in a questionnaire on COVID-19 related symptoms and behaviours. Among 24,861 (40.8%) responders, we invited a random sample of 3,200 individuals for blood testing. Overall, 1,201 (37.5%) individuals were tested for SARS-CoV-2 antibodies (Wantai) and compared to 1,110 active blood donors age 17-69 years. Seroprevalence 95% confidence intervals (CI) were adjusted for assay sensitivity and specificity.

RESULTS: Among retired (age 70 years or older) and active (age 17-69 years) blood donors, adjusted seroprevalences were 1.4% (95% CI: 0.3%-2.5%) and 2.5% (95% CI: 1.3%-3.8%), respectively. Using available population data on COVID-19 related fatalities, IFRs for patients age 70 years or older and for 17-69 years were estimated at 5.4% (95% CI: 2.7%-6.4%) and 0.083% (95% CI: 0.054%-0.18%), respectively. Only 52.4% of SARS-CoV-2 seropositive retired blood donors reported having been sick since the start of the pandemic.

CONCLUSION: COVID-19 IFR in the age group above 69 years is estimated to be 65 times as high as the IFR for people age 18-69 years.

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