TY - JOUR
T1 - Seroprevalence and infection fatality rate of the SARS-CoV-2 Omicron variant in Denmark
T2 - A nationwide serosurveillance study
AU - Erikstrup, Christian
AU - Laksafoss, Anna Damkjær
AU - Gladov, Josephine
AU - Kaspersen, Kathrine Agergård
AU - Mikkelsen, Susan
AU - Hindhede, Lotte
AU - Boldsen, Jens Kjærgaard
AU - Jørgensen, Signe Winther
AU - Ethelberg, Steen
AU - Holm, Dorte Kinggaard
AU - Bruun, Mie Topholm
AU - Nissen, Janna
AU - Schwinn, Michael
AU - Brodersen, Thorsten
AU - Mikkelsen, Christina
AU - Sækmose, Susanne Gjørup
AU - Sørensen, Erik
AU - Harritshøj, Lene Holm
AU - Aagaard, Bitten
AU - Dinh, Khoa Manh
AU - Busch, Michael P
AU - Jørgensen, Charlotte Sværke
AU - Krause, Tyra Grove
AU - Ullum, Henrik
AU - Ostrowski, Sisse Rye
AU - Espenhain, Laura
AU - Pedersen, Ole Birger Vesterager
N1 - © 2022 The Authors.
PY - 2022/10
Y1 - 2022/10
N2 - 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 recently infected residents in the similarly aged background population with no known comorbidity.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% (103/8 701) of donors had detectable anti-N IgG antibodies. Adjusting for test sensitivity (estimates ranging from 74%-81%) and November seroprevalence, we estimate that 66% (95% confidence intervals (CI): 63%-70%) of the healthy, similarly aged Danish population had been infected 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) was 6·2 (CI: 5·1-7·5) 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.
AB - 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 recently infected residents in the similarly aged background population with no known comorbidity.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% (103/8 701) of donors had detectable anti-N IgG antibodies. Adjusting for test sensitivity (estimates ranging from 74%-81%) and November seroprevalence, we estimate that 66% (95% confidence intervals (CI): 63%-70%) of the healthy, similarly aged Danish population had been infected 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) was 6·2 (CI: 5·1-7·5) 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.
UR - http://www.scopus.com/inward/record.url?scp=85135724288&partnerID=8YFLogxK
U2 - 10.1016/j.lanepe.2022.100479
DO - 10.1016/j.lanepe.2022.100479
M3 - Journal article
C2 - 35959415
SN - 2666-7762
VL - 21
JO - The Lancet regional health. Europe
JF - The Lancet regional health. Europe
M1 - 100479
ER -