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 ... -  《-》

Characterization of the SARS-CoV-2 antibody landscape in Norway in the late summer of 2022: high seroprevalence in all age groups with patterns of primary Omicron infection in children and hybrid immunity in adults.

Tunheim G ，Fossum E ，Robertson AH ，Rø GØI ，Chopra A ，Vaage JT ，Vikse EL ，Kran AB ，Magnus P ，Trogstad L ，Mjaaland S ，Hungnes O ，Lund-Johansen F ... -  《BMC INFECTIOUS DISEASES》

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 ... -  《-》

Seroprevalence of SARS-CoV-2-specific anti-spike IgM, IgG, and anti-nucleocapsid IgG antibodies during the second wave of the pandemic: A population-based cross-sectional survey across Kashmir, India.

Within Kashmir, which is one of the topographically distinct areas in the Himalayan belt of India, a total of 2,236 cumulative deaths occurred by the end of the second wave. We aimed to conduct this population-based study in the age group of 7 years and above to estimate the seropositivity and its attributes in Kashmir valley. We conducted a community-based household-level cross-sectional study, with a multistage, population-stratified, probability-proportionate-to-size, cluster sampling method to select 400 participants from each of the 10 districts of Kashmir. We also selected a quota of healthcare workers, police personnel, and antenatal women from each of the districts. Households were selected from each cluster and all family members with age 7 years or more were invited to participate. Information was collected through a standardized questionnaire and entered into Epicollect 5 software. Trained healthcare personnel were assigned for collecting venous blood samples from each of the participants which were transferred and processed for immunological testing. Testing was done for the presence of SARS-CoV-2-specific anti-spike IgM, IgG antibodies, and anti-nucleocapsid IgG antibodies. Weighted seropositivity was estimated along with the adjustment done for the sensitivity and specificity of the test used. The data were collected from a total of 4,229 participants from the general population within the 10 districts of Kashmir. Our results showed that 84.84% (95% CI 84.51-85.18%) of the participants were seropositive in the weighted imputed data among the general population. In multiple logistic regression, the variables significantly affecting the seroprevalence were the age group 45-59 years (odds ratio of 0.73; 95% CI 0.67-0.78), self-reported history of comorbidity (odds ratio of 1.47; 95% CI 1.33-1.61), and positive vaccination history (odds ratio of 0.85; 95% CI 0.79-0.90) for anti-nucleocapsid IgG antibodies. The entire assessed variables showed a significant role during multiple logistic regression analysis for affecting IgM anti-spike antibodies with an odds ratio of 1.45 (95% CI 1.32-1.57) for age more than 60 years, 1.21 (95% CI 1.15-1.27) for the female gender, 0.87 (95% CI 0.82-0.92) for urban residents, 0.86 (95% CI 0.76-0.92) for self-reported comorbidity, and an odds ratio of 1.16 (95% CI 1.08-1.24) for a positive history of vaccination. The estimated infection fatality ratio was 0.033% (95% CI: 0.034-0.032%) between 22 May and 31 July 2021 against the seropositivity for IgM antibodies. During the second wave of the SARS-CoV-2 pandemic, 84.84% (95% CI 84.51-85.18%) of participants from this population-based cross-sectional sample were seropositive against SARS-CoV-2. Despite a comparatively lower number of cases reported and lower vaccination coverage in the region, our study found such high seropositivity across all age groups, which indicates the higher number of subclinical and less severe unnoticed caseload in the community.

Lone KS ，Khan SMS ，Qurieshi MA ，Majid S ，Pandit MI ，Haq I ，Ahmad J ，Bhat AA ，Bashir K ，Bilquees S ，Fazili AB ，Hassan M ，Jan Y ，Kaul RR ，Khan ZA ，Mushtaq B ，Nazir F ，Qureshi UA ，Raja MW ，Rasool M ，Asma A ，Bhat AA ，Chowdri IN ，Ismail S ，Jeelani A ，Kawoosa MF ，Khan MA ，Khan MS ，Kousar R ，Lone AA ，Nabi S ，Qazi TB ，Rather RH ，Sabah I ，Sumji IA ... -  《Frontiers in Public Health》

The seroprevalence of SARS-CoV-2-specific antibodies in Australian children: A cross-sectional study.

Following reduction of public health and social measures concurrent with SARS-CoV-2 Omicron emergence in late 2021 in Australia, COVID-19 case notification rates rose rapidly. As rates of direct viral testing and reporting dropped, true infection rates were most likely to be underestimated. To better understand infection rates and immunity in this population, we aimed to estimate SARS-CoV-2 seroprevalence in Australians aged 0-19 years. We conducted a national cross sectional serosurvey from June 1, 2022, to August 31, 2022, in children aged 0-19 years undergoing an anesthetic procedure at eight tertiary pediatric hospitals. Participant questionnaires were administered, and blood samples tested using the Roche Elecsys Anti-SARS-CoV-2 total spike and nucleocapsid antibody assays. Spike and nucleocapsid seroprevalence adjusted for geographic and socioeconomic imbalances in the participant sample compared to the Australian population was estimated using multilevel regression and poststratification within a Bayesian framework. Blood was collected from 2,046 participants (median age: 6.6 years). The overall adjusted seroprevalence of spike-antibody was 92.1% (95% credible interval (CrI) 91.0-93.3%) and nucleocapsid-antibody was 67.0% (95% CrI 64.6-69.3). In unvaccinated children spike and nucleocapsid antibody seroprevalences were 84.2% (95% CrI 81.9-86.5) and 67.1% (95%CrI 64.0-69.8), respectively. Seroprevalence was similar across geographic remoteness index and socioeconomic quintiles. Nucleocapsid antibody seroprevalence increased with age while the point seroprevalence of the spike antibody seroprevalence decreased in the first year of life and then increased to 97.8 (95% Crl 96.1-99.2) by 12-15 years of age. Most Australian children and adolescents aged 0-19 years, across all jurisdictions were infected with SARS-CoV-2 by August 2022, suggesting rapid and uniform spread across the population in a very short time period. High seropositivity in unvaccinated children informed COVID-19 vaccine recommendations in Australia.

Koirala A ，McRae J ，Britton PN ，Downes M ，Prasad SA ，Nicholson S ，Winkler NE ，O'Sullivan MVN ，Gondalwala F ，Castellano C ，Carey E ，Hendry A ，Crawford N ，Wadia U ，Richmond P ，Marshall HS ，Clark JE ，Francis JR ，Carr J ，Bartlett A ，McMullan B ，Skowno J ，Hannah D ，Davidson A ，von Ungern-Sternberg BS ，Lee-Archer P ，Burgoyne LL ，Waugh EB ，Carlin JB ，Naing Z ，Kerly N ，McMinn A ，Hunter G ，Heath C ，D'Angelo N ，Finucane C ，Francis LA ，Dougherty S ，Rawlinson W ，Karapanagiotidis T ，Cain N ，Brizuela R ，Blyth CC ，Wood N ，Macartney K ... -  《PLoS One》