Download This Paper
Preprints with The Lancet is a collaboration between The Lancet Group of journals and SSRN to facilitate the open sharing of preprints for early engagement, community comment, and collaboration. Preprints available here are not Lancet publications or necessarily under review with a Lancet journal. These preprints are early-stage research papers that have not been peer-reviewed. The usual SSRN checks and a Lancet-specific check for appropriateness and transparency have been applied. The findings should not be used for clinical or public health decision-making or presented without highlighting these facts. For more information, please see the FAQs.
Estimation of the Seroprevalence and Infection Fatality Rate of the SARS-CoV-2 Omicron Variant Using Antibody Screening of Danish Blood Donors
24 Pages Posted: 16 May 2022
More...Abstract
Background: Introduction of the Omicron variant caused a steep rise in SARS-CoV-2 infections despite high vaccination-coverage in the Danish population. We used blood donor serosurveillance to estimate the percentage of the population with recent infection.
Methods: To detect SARS-CoV-2 antibodies induced due to recent infection, and not vaccination, we assessed anti-nucleocapsid (anti-N) immunoglobulin G (IgG) in blood donor samples. Individual level data on SARS-CoV-2 RT-PCR results and vaccination status were available. Anti-N IgG was measured fortnightly from January 18 to April 3, 2022. Samples from November 2021 were analysed to assess seroprevalence before introduction of the Omicron variant in Denmark.
Findings: A total of 43 088 donations from 35 309 Danish blood donors aged 17–72 years were screened. In November 2021, 1∙2 % of donors had detectable anti-N IgG antibodies. With adjustment for test sensitivity (estimates ranging from 74%–81%) and November seroprevalence, we estimate that 68% (95% confidence intervals (CI): 64%–71%) of the healthy adult Danish population had been infected with SARS-CoV-2 between November 1, 2021, and March 15, 2022. One third of infections were not captured by SARS-CoV-2 RT-PCR testing. The infection fatality rate (IFR) among the healthy adult Danish population was 6 (CI: 5–7) per 100 000 infections.
Interpretation: Screening for anti-N IgG and linkage to national registers allowed us to detect recent infections and accurately assess assay sensitivity in vaccinated or previously infected individuals during the Omicron outbreak. The IFR was lower than during previous waves.
Funding: The Danish Ministry of Health
Declaration of Interest: The authors declare no conflict of interests
Ethical Approval: The study was approved as a surveillance study in all five Danish administrative regions and the appropriate institutional forms obtained
Suggested Citation: Suggested Citation