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

Infection 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. Residual 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. Antibodies 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. 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.

Tunheim G ，Rø GØI ，Tran T ，Kran AB ，Andersen JT ，Vaage EB ，Kolderup A ，Vaage JT ，Lund-Johansen F ，Hungnes O ... -  《-》

Prevalence of antibodies against SARS-CoV-2 in the Norwegian population, August 2021.

One year into the COVID-19 pandemic, the cumulative number of confirmed COVID-19 cases in Norway was still low. In January 2021, when the Norwegian COVID-19 vaccination campaign started, the national seroprevalence estimate of SARS-CoV-2 antibodies was 3.2%. We have conducted a nationwide cross-sectional study in August 2021 to investigate the overall prevalence of SARS-CoV-2 antibodies in Norway after 8 months of COVID-19 mass vaccination and a third wave of SARS-CoV-2 infection. Residual sera were collected from laboratories across Norway in August 2021. In IgG antibodies against the spike protein, the spike receptor binding domain (RBD) and the nucleocapsid protein of SARS-CoV-2 were measured by a bead-based flow cytometric assay. In total, 1926 residual sera were collected from individuals aged 0-98 years; 55.1% were from women. The overall national estimated seroprevalence from vaccination and/or infection was 62.6% (credible interval [CrI] 60.1%-65.2%) based on having antibodies against both spike and RBD. Estimated seroprevalence increased with age. Among all samples, 11.7% had antibodies against nucleocapsid. For unvaccinated children <12 years, the seroprevalence estimate due to SARS-CoV-2 infection was 12.5% (95% CrI 9.3%-16.1%). Of seropositive samples from the unvaccinated children, 31.9% lacked anti-nucleocapsid antibodies. The high overall SARS-CoV-2 seroprevalence estimates are in line with Norwegian registry data. Vaccination, not infection, contributed the most to the high seroprevalence in August 2021. Lack of antibodies against nucleocapsid should not automatically be interpreted as absence of previous infection as this could lead to underestimation of COVID-19 cases in seroprevalence studies.

Tunheim G ，Rø GØI ，Chopra A ，Aase A ，Kran AB ，Vaage JT ，Lund-Johansen F ，Hungnes O ... -  《-》

Estimating global, regional, and national daily and cumulative infections with SARS-CoV-2 through Nov 14, 2021: a statistical analysis.

COVID-19 Cumulative Infection Collaborators 《-》

Estimated SARS-CoV-2 infection rate and fatality risk in Gauteng Province, South Africa: a population-based seroepidemiological survey.

Limitations in laboratory testing capacity undermine the ability to quantify the overall burden of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. We undertook a population-based serosurvey for SARS-CoV-2 infection in 26 subdistricts, Gauteng Province (population 15.9 million), South Africa, to estimate SARS-CoV-2 infection, infection fatality rate (IFR) triangulating seroprevalence, recorded COVID-19 deaths and excess-mortality data. We employed three-stage random household sampling with a selection probability proportional to the subdistrict size, stratifying the subdistrict census-sampling frame by housing type and then selecting households from selected clusters. The survey started on 4 November 2020, 8 weeks after the end of the first wave (SARS-CoV-2 nucleic acid amplification test positivity had declined to <10% for the first wave) and coincided with the peak of the second wave. The last sampling was performed on 22 January 2021, which was 9 weeks after the SARS-CoV-2 resurgence. Serum SARS-CoV-2 receptor-binding domain (RBD) immunoglobulin-G (IgG) was measured using a quantitative assay on the Luminex platform. From 6332 individuals in 3453 households, the overall RBD IgG seroprevalence was 19.1% [95% confidence interval (CI): 18.1-20.1%] and similar in children and adults. The seroprevalence varied from 5.5% to 43.2% across subdistricts. Conservatively, there were 2 897 120 (95% CI: 2 743 907-3 056 866) SARS-CoV-2 infections, yielding an infection rate of 19 090 per 100 000 until 9 January 2021, when 330 336 COVID-19 cases were recorded. The estimated IFR using recorded COVID-19 deaths (n = 8198) was 0.28% (95% CI: 0.27-0.30) and 0.67% (95% CI: 0.64-0.71) assuming 90% of modelled natural excess deaths were due to COVID-19 (n = 21 582). Notably, 53.8% (65/122) of individuals with previous self-reported confirmed SARS-CoV-2 infection were RBD IgG seronegative. The calculated number of SARS-CoV-2 infections was 7.8-fold greater than the recorded COVID-19 cases. The calculated SARS-CoV-2 IFR varied 2.39-fold when calculated using reported COVID-19 deaths (0.28%) compared with excess-mortality-derived COVID-19-attributable deaths (0.67%). Waning RBD IgG may have inadvertently underestimated the number of SARS-CoV-2 infections and conversely overestimated the mortality risk. Epidemic preparedness and response planning for future COVID-19 waves will need to consider the true magnitude of infections, paying close attention to excess-mortality trends rather than absolute reported COVID-19 deaths.

Mutevedzi PC ，Kawonga M ，Kwatra G ，Moultrie A ，Baillie V ，Mabena N ，Mathibe MN ，Rafuma MM ，Maposa I ，Abbott G ，Hugo J ，Ikalafeng B ，Adelekan T ，Lukhele M ，Madhi SA ... -  《-》

Seroprevalence of SARS-CoV-2 infection in the general population of Nepal during the first and second generalized waves of the COVID-19 pandemic-2020-2021.

Paudel KP ，Samuel R ，Jha R ，Pandey BD ，Edirisuriya C ，Shrestha NL ，Gyawali P ，Pokhrel A ，Shrestha L ，Mahato RK ，Hossain SS ，Arunkumar G ，Bose AS ，Dhimal M ，Gautam D ，Neupane S ，Thakur N ，Shrestha S ，Bhusal N ，Jha P ，Gupta BP ，Rayamajhi RB ，Subedi KC ，Kandel S ，Poudel M ，Thapa LB ，Sharma GN ，Gocotano AE ，Sunny AK ，Gautam R ，Bhatta DR ，Awale BK ，Roka B ，Ojha HC ，Baral P ，Adhikari MD ，Lohani GR ，Shrestha M ，Singh DR ，Aryal L ，Pandav RS ，Pokhrel R ... -  《-》