Trends in seroprevalence of SARS-CoV-2 and infection fatality rate in the Norwegian population through the first year of the COVID-19 pandemic.

Gro Tunheim,Jan Terje Andersen,John Torgils Vaage,Eline Benno Vaage,Gunnar Øyvind Isaksson Rø,Anette Kolderup,Trung Tran,Fridtjof Lund‐Johansen,Olav Hungnes,Anne‐Marte Bakken Kran

doi:10.1111/irv.12932

Abstract

BackgroundInfection with the novel coronavirus SARS‐CoV‐2 induces antibodies that can be used as a proxy for COVID‐19. We present a repeated nationwide cross‐sectional study assessing the seroprevalence of SARS‐CoV‐2, the infection fatality rate (IFR), and infection hospitalization rate (IHR) during the first year of the pandemic in Norway.MethodsResidual serum samples were solicited in April/May 2020 (Round 1), in July/August 2020 (Round 2) and in January 2021 (Round 3). Antibodies against SARS‐CoV‐2 were measured using a flow cytometer‐based assay. Aggregate data on confirmed cases, COVID‐19‐associated deaths and hospitalizations were obtained from the Emergency preparedness registry for COVID‐19 (Beredt C19), and the seroprevalence estimates were used to estimate IFR and IHR.ResultsAntibodies against SARS‐CoV‐2 were measured in 4840 samples. The estimated seroprevalence increased from 0.8% (95% credible interval [CrI] 0.4%–1.3%) after the first wave of the pandemic (Rounds 1 and 2 combined) to 3.2% (95% CrI 2.3%–4.2%) (Round 3). The IFR and IHR were higher in the first wave than in the second wave and increased with age. The IFR was 0.2% (95% CrI 0.1%–0.3%), and IHR was 0.9% (95% CrI 0.6%–1.5%) for the second wave.ConclusionsThe seroprevalence estimates show a cumulative increase of SARS‐CoV‐2 infections over time in the Norwegian population and suggest some under‐recording of confirmed cases. The IFR and IHR were low, corresponding to the relatively low number of COVID‐19‐associated deaths and hospitalizations in Norway. Most of the Norwegian population was still susceptible to SARS‐CoV‐2 infection after the first year of the pandemic.

Highlights

On 11 March 2020, the World Health Organization (WHO) assessed that coronavirus disease 2019 (COVID-19) should be characterized as a pandemic.[1]
According to the number of confirmed cases of COVID-19 reported to MSIS, the pandemic was quite contained in Norway during the summer of 2020, after the peak of the pandemic in March.[2]
We combined the data from Rounds 1 and 2 to obtain a more robust seroprevalence estimate with a larger sample size representing the seroprevalence estimate after the first wave of the pandemic in Norway

Summary

Introduction

On 11 March 2020, the World Health Organization (WHO) assessed that coronavirus disease 2019 (COVID-19) should be characterized as a pandemic.[1]. In the autumn of 2020, the numbers of confirmed COVID-19 cases again started rising, representing a second wave of the pandemic, a pattern observed in other European countries.[2,5] In the first week of January 2021, there was a new peak in the incidence of COVID-19 cases in Norway, followed by a decline probably due to additional non-pharmaceutical measures. We present a repeated nationwide crosssectional study assessing the seroprevalence of SARS-CoV-2, the infection fatality rate (IFR), and infection hospitalization rate (IHR) during the first year of the pandemic in Norway. Conclusions: The seroprevalence estimates show a cumulative increase of SARS-CoV-2 infections over time in the Norwegian population and suggest some under-recording of confirmed cases. The IFR and IHR were low, corresponding to the relatively low number of COVID-19-associated deaths and hospitalizations in Norway. Most of the Norwegian population was still susceptible to SARS-CoV-2 infection after the first year of the pandemic

Results

Discussion

Conclusion