Research Open Access
Like 0



Since March 2020, 440 million people worldwide have been diagnosed with COVID-19, but the true number of infections with SARS-CoV-2 is higher. SARS-CoV-2 antibody seroprevalence can add crucial epidemiological information about population infection dynamics.


To provide a large population-based SARS-CoV-2 seroprevalence survey from Norway; we estimated SARS-CoV-2 seroprevalence before introduction of vaccines and described its distribution across demographic groups.


In this population-based cross-sectional study, a total of 110,000 people aged 16 years or older were randomly selected during November–December 2020 and invited to complete a questionnaire and provide a dried blood spot (DBS) sample.


The response rate was 30% (31,458/104,637); compliance rate for return of DBS samples was 88% (27,700/31,458). National weighted and adjusted seroprevalence was 0.9% (95% CI (confidence interval): 0.7–1.0). Seroprevalence was highest among those aged 16–19 years (1.9%; 95% CI: 0.9–2.9), those born outside the Nordic countries 1.4% (95% CI: 1.0–1.9), and in the counties of Oslo 1.7% (95% CI: 1.2–2.2) and Vestland 1.4% (95% CI: 0.9–1.8). The ratio of SARS-CoV-2 seroprevalence (0.9%) to cumulative incidence of virologically detected cases by mid-December 2020 (0.8%) was slightly above one. SARS-CoV-2 seroprevalence was low before introduction of vaccines in Norway and was comparable to virologically detected cases, indicating that most cases in the first 10 months of the pandemic were detected.


Findings suggest that preventive measures including contact tracing have been effective, people complied with physical distancing recommendations, and local efforts to contain outbreaks have been essential.


Article metrics loading...

Loading full text...

Full text loading...



  1. Johns Hopkins University and Medicine (JHU). COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. Baltimore: JHU. [Accessed: 23 Mar 2021]. Available from: https://coronavirus.jhu.edu/map.html
  2. Eckerle I, Meyer B. SARS-CoV-2 seroprevalence in COVID-19 hotspots. Lancet. 2020;396(10250):514-5.  https://doi.org/10.1016/S0140-6736(20)31482-3  PMID: 32645348 
  3. Oran DP, Topol EJ. The proportion of SARS-CoV-2 infections that are asymptomatic: a systematic review. Ann Intern Med. 2021;174(5):655-62.  https://doi.org/10.7326/M20-6976  PMID: 33481642 
  4. Lai CC, Wang JH, Hsueh PR. Population-based seroprevalence surveys of anti-SARS-CoV-2 antibody: An up-to-date review. Int J Infect Dis. 2020;101:314-22.  https://doi.org/10.1016/j.ijid.2020.10.011  PMID: 33045429 
  5. Jacofsky D, Jacofsky EM, Jacofsky M. Understanding antibody testing for COVID-19. J Arthroplasty. 2020;35(7S) 7S;S74-81.  https://doi.org/10.1016/j.arth.2020.04.055  PMID: 32389405 
  6. Murin CD, Wilson IA, Ward AB. Antibody responses to viral infections: a structural perspective across three different enveloped viruses. Nat Microbiol. 2019;4(5):734-47.  https://doi.org/10.1038/s41564-019-0392-y  PMID: 30886356 
  7. Wang Y, Li J, Li H, Lei P, Shen G, Yang C. Persistence of SARS-CoV-2-specific antibodies in COVID-19 patients. Int Immunopharmacol. 2021;90:107271.  https://doi.org/10.1016/j.intimp.2020.107271  PMID: 33310664 
  8. Chen X, Chen Z, Azman AS, Deng X, Sun R, Zhao Z, et al. Serological evidence of human infection with SARS-CoV-2: a systematic review and meta-analysis. Lancet Glob Health. 2021;9(5):e598-609.  https://doi.org/10.1016/S2214-109X(21)00026-7  PMID: 33705690 
  9. Norwegian Institute of Public Health (NIPH). Statistikk om koronavirus og covid-19. [Statistics about coronavirus and Covid-19]. Oslo: NIPH. [Accessed: 4 March 2021]. Norwegian. Available from: https://www.fhi.no/sv/smittsomme-sykdommer/corona/dags--og-ukerapporter/dags--og-ukerapporter-om-koronavirus
  10. Tunheim G, Bakken A-M, Rø KG, Hungnes O, Lund-Johansen F, Tran T, et al. Seroprevalence of SARS-CoV-2 in the Norwegian population measured in residual sera collected in late summer 2020. Oslo: Norwegian Institute for Public Health; 2020.
  11. Tunheim G, Kran A-MB, Rø G, Steens A, Hungnes O, Lund-Johansen F, et al. Seroprevalence of SARS-CoV-2 in the Norwegian population measured in residual sera collected in April/May 2020 and August 2019. Oslo: Norwegian Institute for Public Health; 2020.
  12. Norwegian Institute of Public Health (NIPH). Resultater fra MoBa og Norflu. Hvor mange var smittet med koronavirus i Oslo og omegn i 2020? [Results from MoBa and NORFLU. How many have been infected by the Covid-19 virus in Oslo and the suburbs in 2020?]. Oslo: NIPH; 2020. Norwegian. Available from: https://www.fhi.no/studier/prevalensundersokelser-korona/resultat---moba
  13. Statistics Norway. Fakta om befolkningen. [Facts about the population]. Oslo: Statistics Norway; 2021. Norwegian. Available from: https://www.ssb.no/befolkning/faktaside/befolkningen
  14. Abrahamsen R, Svendsen MV, Henneberger PK, Gundersen GF, Torén K, Kongerud J, et al. Non-response in a cross-sectional study of respiratory health in Norway. BMJ Open. 2016;6(1):e009912.  https://doi.org/10.1136/bmjopen-2015-009912  PMID: 26739738 
  15. Zava TT, Zava DT. Validation of dried blood spot sample modifications to two commercially available COVID-19 IgG antibody immunoassays. Bioanalysis. 2021;13(1):13-28.  https://doi.org/10.4155/bio-2020-0289  PMID: 33319585 
  16. Valliant R, Dever JA. Survey Weights: A Step-by-step Guide to Calculation. Stata Press; 2018.
  17. Diggle PJ. Estimating prevalence using an imperfect test. Epidemiol Res Int. 2011;2011:1-5.  https://doi.org/10.1155/2011/608719 
  18. Helsingen LM, Løberg M, Refsum E, Gjøstein DK, Wieszczy P, Olsvik Ø, et al. Covid-19 transmission in fitness centers in Norway - a randomized trial. BMC Public Health. 2021;21(1):2103.  https://doi.org/10.1186/s12889-021-12073-0  PMID: 34789188 
  19. Ward H, Atchison C, Whitaker M, Ainslie KEC, Elliott J, Okell L, et al. SARS-CoV-2 antibody prevalence in England following the first peak of the pandemic. Nat Commun. 2021;12(1):905.  https://doi.org/10.1038/s41467-021-21237-w  PMID: 33568663 
  20. European Centre for Disease Prevention and Control (ECDC). COVID-19 in children and the role of school settings in transmission - first update. Stockholm: ECDC; 23 Dec 2020. Available from: https://www.ecdc.europa.eu/sites/default/files/documents/COVID-19-in-children-and-the-role-of-school-settings-in-transmission-first-update_1.pdf
  21. Duysburgh E, Mortgat L, Barbezange C, Dierick K, Fischer N, Heyndrickx L, et al. Persistence of IgG response to SARS-CoV-2. Lancet Infect Dis. 2021;21(2):163-4.  https://doi.org/10.1016/S1473-3099(20)30943-9  PMID: 33341124 
  22. Li C, Yu D, Wu X, Liang H, Zhou Z, Xie Y, et al. Twelve-month specific IgG response to SARS-CoV-2 receptor-binding domain among COVID-19 convalescent plasma donors in Wuhan. Nat Commun. 2021;12(1):4144.  https://doi.org/10.1038/s41467-021-24230-5  PMID: 34230476 
  23. Norwegian Institute of Public Health (NIPH). Daily report and statistics about coronavirus and COVID-19. Oslo: NIPH. [Accessed: 11 Mar 2022]. Available from: https://www.fhi.no/en/id/infectious-diseases/coronavirus/daily-reports/daily-reports-COVID19
  24. Turgeon CT, Sanders KA, Granger D, Nett SL, Hilgart H, Matern D, et al. Detection of SARS-CoV-2 IgG antibodies in dried blood spots. Diagn Microbiol Infect Dis. 2021;101(1):115425-115425.  https://doi.org/10.1016/j.diagmicrobio.2021.115425  PMID: 34116343 
  25. Cheung KL, Ten Klooster PM, Smit C, de Vries H, Pieterse ME. The impact of non-response bias due to sampling in public health studies: A comparison of voluntary versus mandatory recruitment in a Dutch national survey on adolescent health. BMC Public Health. 2017;17(1):276.  https://doi.org/10.1186/s12889-017-4189-8  PMID: 28330465 
  26. Hansen CH, Michlmayr D, Gubbels SM, Mølbak K, Ethelberg S. Assessment of protection against reinfection with SARS-CoV-2 among 4 million PCR-tested individuals in Denmark in 2020: a population-level observational study. Lancet. 2021;397(10280):1204-12.  https://doi.org/10.1016/S0140-6736(21)00575-4  PMID: 33743221 
  27. Willis BH. Spectrum bias--why clinicians need to be cautious when applying diagnostic test studies. Fam Pract. 2008;25(5):390-6.  https://doi.org/10.1093/fampra/cmn051  PMID: 18765409 
  28. Jacobsen FF, Arntzen C, Devik SA, Førland O, Krane MS, Madsen L, et al. Erfaringer med COVID-19 i norske sykehjem. [Covid-19 infections in Norwegian nursing homes and lessons learned from Covid-19 infections in Norwegian nursing homes]. Gjøvik: Senter for omsorgsforskning; 2021. Norwegian. Available from: https://omsorgsforskning.brage.unit.no/omsorgsforskning-xmlui/handle/11250/2737650

Data & Media loading...

Supplementary data

Submit comment
Comment moderation successfully completed
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error