Seroprevalence of and risk factors for feline coronavirus infection in cats from Greece.

Feline coronavirus (FCoV) is a highly contagious and ubiquitous virus of domestic cats and wild felids. Feline infectious peritonitis (FIP) is a fatal, systemic disease caused by FCoV infection when spontaneous mutations of the viral genome take place. The aims of this study were primarily to determine the prevalence of seropositivity for FCoV in different populations of cats in Greece and assess risk factors for seropositivity. A total of 453 cats were prospectively enrolled in the study. A commercially available IFAT kit was used for the detection of FCoV IgG antibodies in serum. Overall, 55 (12.1 %) of the 453 cats were seropositive for FCoV. Based on multivariable analysis, factors associated with FCoV-seropositivity included cats adopted as strays and contact with other cats. This is the first extensive study on the epidemiology of FCoV in cats from Greece and one of the largest worldwide. Feline coronavirus infection is relatively common in Greece. Therefore, it is necessary to establish optimal strategies for the prevention of FCoV infection, considering the high-risk groups of cats identified in this study.

Seroprevalence of COVID-19 infection in a densely populated district in the eastern Democratic Republic of Congo.

Data on coronavirus disease 2019 (COVID-19) prevalence in the Democratic Republic of Congo are scarce. We conducted a cross-sectional study to determine the seroprevalence of antibodies against anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the slum of Kadutu, city of Bukavu, between June and September 2021. The survey participants were all unvaccinated against SARS-CoV-2. The crude seroprevalence rate was adjusted to the known characteristics of the assay. Participants aged 15-49 years old made up 80% of the population enrolled in the study (n = 507; 319 women and 188 men). The overall crude and adjusted seroprevalence rates of antibodies for COVID-19 were 59.7% (95% CI 55.4-63.9%) and 84.0% (95% CI 76.2-92.4%), respectively. This seroprevalence rate indicates widespread dissemination of SARS-CoV-2 in these communities. COVID-19 symptoms were either absent or mild in more than half of the participants with antibodies for COVID-19 and none of the participants with antibodies for COVID-19 required hospitalisation. These results suggest that SARS-CoV-2 spread did not appear to be associated with severe symptoms in the population of these settlements and that many cases went unreported in these densely populated locations. The relevance of vaccination in these communities should be thoroughly investigated.

Heterogeneous evolution of SARS-CoV-2 seroprevalence in school-age children: Results from the school-based cohort study Ciao Corona in November-December 2021 in the canton of Zurich.

BACKGROUND: Much remains unknown regarding the evolution of SARS-CoV-2 seroprevalence and variability in seropositive children in districts, schools and classes as only a few school-based cohort studies exist. Vaccination of children, initiated at different times for different age groups, adds additional complexity to the understanding of how seroprevalence developed in the school aged population. AIM: We investigated the evolution of SARS-CoV-2 seroprevalence in children and its variability in districts, schools and classes in Switzerland from June/July 2020 to November/December 2021. METHODS: In this school-based cohort study, SARS-CoV-2 antibodies were measured in primary and secondary school children from randomly selected schools in the canton of Zurich in October/November 2020, March/April 2021 and November/December 2021. Seroprevalence was estimated using Bayesian logistic regression to adjust for test sensitivity and specificity. Variability of seroprevalence between school classes was expressed as maximum minus minimum seroprevalence in a class and summarised as median (interquartile range). RESULTS: 1875 children from 287 classes in 43 schools were tested, with median age 12 years (range 6-17), 51% 12+ vaccinated. Seroprevalence increased from 5.6% (95% credible interval [CrI] 3.5-7.6%) to 31.1% (95% CrI 27.0-36.1%) in unvaccinated children, and 46.4% (95% CrI 42.6-50.9%) in all children (including vaccinated). Earlier in the pandemic, seropositivity rates in primary schools were similar to or slightly higher (<5%) than those in secondary schools, but by late 2021, primary schools had 12.3% (44.3%) lower seroprevalence for unvaccinated (all) subjects. Variability in seroprevalence among districts and schools increased more than two-fold over time, and in classes from 11% (95% CrI 7-17%) to 40% (95% CrI 22-49%). CONCLUSIONS: Seroprevalence in children increased greatly, especially in 2021 following introduction of vaccines. Variability in seroprevalence was high and increased substantially over time, suggesting complex transmission chains.

Low Prevalence of SARS-CoV-2 Antibodies in Canine and Feline Serum Samples Collected during the COVID-19 Pandemic in Hong Kong and Korea.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected millions of people worldwide since its emergence in 2019. Knowing the potential capacity of the virus to adapt to other species, the serological surveillance of SARS-CoV-2 infection in susceptible animals is important. Hong Kong and Seoul are two of Asia's most densely populated urban cities, where companion animals often live in close contact with humans. Sera collected from 1040 cats and 855 dogs during the early phase of the pandemic in Hong Kong and Seoul were tested for SARS-CoV-2 antibodies using an ELISA that detects antibodies against the receptor binding domain of the viral spike protein. Positive sera were also tested for virus neutralizing antibodies using a surrogate virus neutralization (sVNT) and plaque reduction neutralization test (PRNT). Among feline sera, 4.51% and 2.54% of the samples from Korea and Hong Kong, respectively, tested ELISA positive. However, only 1.64% of the samples from Korea and 0.18% from Hong Kong tested positive by sVNT, while only 0.41% of samples from Korea tested positive by PRNT. Among canine samples, 4.94% and 6.46% from Korea and Hong Kong, respectively, tested positive by ELISA, while only 0.29% of sera from Korea were positive on sVNT and no canine sera tested positive by PRNT. These results confirm a low seroprevalence of SARS-CoV-2 exposure in companion animals in Korea and Hong Kong. The discordance between the RBD-ELISA and neutralization tests may indicate possible ELISA cross-reactivity with other coronaviruses, especially in canine sera.

A Cross-Sectional Study of SARS-CoV-2 Antibodies and Risk Factors for Seropositivity in Staff in Day Care Facilities and Preschools in Denmark.

The aim of this study was to provide information about immunity against COVID-19 along with risk factors and behavior among employees in day care facilities and preschools (DCS) in Denmark. In collaboration with the Danish Union of Pedagogues, during February and March 2021, 47,810 members were offered a point-of-care rapid SARS-CoV-2 antibody test (POCT) at work and were invited to fill in an electronic questionnaire covering COVID-19 exposure. Seroprevalence data from Danish blood donors (total Ig enzyme-linked immunosorbent assay [ELISA]) were used as a proxy for the Danish population. A total of 21,018 (45%) DCS employees completed the questionnaire and reported their POCT result {median age, 44.3 years (interquartile range [IQR], [32.7 to 53.6]); females, 84.1%}, of which 20,267 (96.4%) were unvaccinated and included in analysis. A total of 1,857 (9.2%) participants tested seropositive, significantly higher than a seroprevalence at 7.6% (risk ratio [RR], 1.2; 95% confidence interval [CI], 1.14 to 1.27) among 40,541 healthy blood donors (median age, 42 years [IQR, 28 to 53]; males, 51.3%). Exposure at work (RR, 2.9; 95% CI, 2.3 to 3.6) was less of a risk factor than exposure within the household (RR, 12.7; 95% CI, 10.2 to 15.8). Less than 25% of participants reported wearing face protection at work. Most of the participants expressed some degree of fear of contracting COVID-19 both at work and outside work. SARS-CoV-2 seroprevalence was slightly higher in DCS staff than in blood donors, but possible exposure at home was associated with a higher risk than at work. DCS staff expressed fear of contracting COVID-19, though there was limited use of face protection at work. IMPORTANCE Identifying at-risk groups and evaluating preventive interventions in at-risk groups is imperative for the ongoing pandemic as well as for the control of future epidemics. Although DCS staff have a much higher risk of being infected within their own household than at their workplace, most are fearful of being infected with COVID-19 or bringing COVID-19 to work. This represents an interesting dilemma and an important issue which should be addressed by public health authorities for risk communication and pandemic planning. This study design can be used in a strategy for ongoing surveillance of COVID-19 immunity or other infections in the population. The findings of this study can be used to assess the need for future preventive interventions in DCS, such as the use of personal protective equipment.

Seroprevalence of Antibodies to SARS-CoV-2 in Rural Households in Eastern Uganda, 2020-2022.

Importance: Estimating the true burden of SARS-CoV-2 infection has been difficult in sub-Saharan Africa owing to asymptomatic infections and inadequate testing capacity. Antibody responses from serologic surveys can provide an estimate of SARS-CoV-2 exposure at the population level. Objective: To estimate SARS-CoV-2 seroprevalence, attack rates, and reinfection in eastern Uganda using serologic surveillance from 2020 to early 2022. Design, Setting, and Participants: This cohort study was conducted in the Tororo and Busia districts of eastern Uganda. Plasma samples from participants in the Program for Resistance, Immunology, Surveillance, and Modeling of Malaria in Uganda Border Cohort were obtained at 4 sampling intervals: October to November 2020, March to April 2021, August to September 2021, and February to March 2022. Each participant contributed up to 4 time points for SARS-CoV-2 serology, with almost half of all participants contributing at all 4 time points, and almost 90% contributing at 3 or 4 time points. Information on SARS-CoV-2 vaccination status was collected from participants, with the earliest reported vaccinations in the cohort occurring in May 2021. Main Outcomes and Measures: The main outcomes of this study were antibody responses to the SARS-CoV-2 spike protein as measured with a bead-based serologic assay. Individual-level outcomes were aggregated to population-level SARS-CoV-2 seroprevalence, attack rates, and boosting rates. Estimates were weighted by the local age distribution according to census data. Results: A total of 1483 samples from 441 participants living in 76 households were tested. Of the 441 participants, 245 (55.6%) were female, and their mean (SD) age was 16.04 (16.04) years. By the end of the Delta wave and before widespread vaccination, adjusted SARS-CoV-2 seroprevalence was 67.7% (95% credible interval [CrI], 62.5%-72.6%) in the study population. During the subsequent Omicron wave, 84.8% (95% CrI, 67.9%-93.7%) of unvaccinated, previously seronegative individuals were infected for the first time, and 50.8% (95% CrI, 40.6%-59.7%) of unvaccinated, already seropositive individuals were likely reinfected, leading to an overall seropositivity of 96.0% (95% CrI, 93.4%-97.9%) in this population. These results suggest a lower probability of reinfection in individuals with higher preexisting antibody levels. There was evidence of household clustering of SARS-CoV-2 seroconversion. No significant associations were found between SARS-CoV-2 seroconversion and gender, household size, or recent Plasmodium falciparum malaria exposure. Conclusions and Relevance: In this cohort study in a rural population in eastern Uganda, there was evidence of very high SARS-CoV-2 infection rates throughout the pandemic inconsistent with national level case data and high reinfection rates during the Omicron wave.

National seroepidemiological study of COVID-19 after the initial rollout of vaccines: Before and at the peak of the Omicron-dominant period in Japan.

Background: Based on routine surveillance data, Japan has been affected much less by COVID-19 compared with other countries. To validate this, we aimed to estimate SARS-CoV-2 seroprevalence and examine sociodemographic factors associated with cumulative infection in Japan. Methods: A population-based serial cross-sectional seroepidemiological investigation was conducted in five prefectures in December 2021 (pre-Omicron) and February-March 2022 (Omicron [BA.1/BA.2]-peak). Anti-nucleocapsid and anti-spike antibodies were measured to detect infection-induced and vaccine/infection-induced antibodies, respectively. Logistic regression was used to identify associations between various factors and past infection. Results: Among 16 296 participants (median age: 53 [43-64] years), overall prevalence of infection-induced antibodies was 2.2% (95% CI: 1.9-2.5%) in December 2021 and 3.5% (95% CI: 3.1-3.9%) in February-March 2022. Factors associated with past infection included those residing in urban prefectures (Tokyo: aOR 3.37 [95% CI: 2.31-4.91], Osaka: aOR 3.23 [95% CI: 2.17-4.80]), older age groups (60s: aOR 0.47 [95% CI 0.29-0.74], 70s: aOR 0.41 [95% CI 0.24-0.70]), being vaccinated (twice: aOR 0.41 [95% CI: 0.28-0.61], three times: aOR 0.21 [95% CI: 0.12-0.36]), individuals engaged in occupations such as long-term care workers (aOR: 3.13 [95% CI: 1.47-6.66]), childcare workers (aOR: 3.63 [95% CI: 1.60-8.24]), food service workers (aOR: 3.09 [95% CI: 1.50-6.35]), and history of household contact (aOR: 26.4 [95% CI: 20.0-34.8]) or non-household contact (aOR: 5.21 [95% CI:3.80-7.14]) in February-March 2022. Almost all vaccinated individuals (15 670/15 681) acquired binding antibodies with higher titers among booster dose recipients. Conclusions: Before Omicron, the cumulative burden was >10 times lower in Japan (2.2%) compared with the US (33%), the UK (25%), or global estimates (45%), but most developed antibodies owing to vaccination.

Trajectories of Seroprevalence and Neutralizing Activity of Antibodies against SARS-CoV-2 in Southern Switzerland between July 2020 and July 2021: An Ongoing, Prospective Population-Based Cohort Study.

OBJECTIVES: The COVID-19 pandemic continues, and evidence on infection- and vaccine-induced immunity is key. We assessed COVID-19 immunity and the neutralizing antibody response to virus variants across age groups in the Swiss population. STUDY DESIGN: We conducted a cohort study in representative community-dwelling residents aged five years or older in southern Switzerland (total population 353,343), and we collected blood samples in July 2020 (in adults only, N = 646), November-December 2020 (N = 1457), and June-July 2021 (N = 885). METHODS: We used a previously validated Luminex assay to measure antibodies targeting the spike (S) and the nucleocapsid (N) proteins of the virus and a high-throughput cell-free neutralization assay optimized for multiple spike protein variants. We calculated seroprevalence with a Bayesian logistic regression model accounting for the population's sociodemographic structure and the test performance, and we compared the neutralizing activity between vaccinated and convalescent participants across virus variants. RESULTS: The overall seroprevalence was 7.8% (95% CI: 5.4-10.4) by July 2020 and 20.2% (16.4-24.4) by December 2020. By July 2021, the overall seroprevalence increased substantially to 72.5% (69.1-76.4), with the highest estimates of 95.6% (92.8-97.8) among older adults, who developed up to 10.3 more antibodies via vaccination than after infection compared to 3.7 times more in adults. The neutralizing activity was significantly higher for vaccine-induced than infection-induced antibodies for all virus variants (all p values < 0.037). CONCLUSIONS: Vaccination chiefly contributed to the reduction in immunonaive individuals, particularly those in older age groups. Our findings on the greater neutralizing activity of vaccine-induced antibodies than infection-induced antibodies are greatly informative for future vaccination campaigns.

Seroprevalence of Anti-SARS-CoV-2 Antibodies Following the Omicron BA.1 Wave.

We conducted a seroprevalence study using convenient residual sera samples from the Slovenian population collected after the end of the Omicron BA.1 pandemic wave. Serum samples were tested for spike glycoprotein (anti-S) and nucleocapsid protein (anti-N) antibodies. Participants' data regarding confirmed infection and vaccination was obtained from national registries. Anti-S antibodies were detected in 2439 (84.1%) of 2899 sera from persons aged 0-90 years, with the lowest prevalence in the 0-17 age group. The proportion of anti-N positives was the lowest in the ≥70 age group. The proportion of anti-N positives was significantly higher among participants with confirmed past infection and among those who had never been vaccinated. In participants who had not been notified as infected and who had never been vaccinated, the seroprevalence of anti-S and anti-N antibodies was 53% and 35.5%, respectively. From the time of serum collection to mid-November 2022, 445 participants (15.3%) tested positive for SARS-CoV-2, with higher odds in seronegative participants, participants in the 40-59 age group, and those without notified previous infection. Vaccination status and gender had no significant effects on infection risk. This study underlines the importance of serosurveys in understanding the development of the pandemic.

Seroprevalence of four endemic human coronaviruses and, reactivity and neutralization capability against SARS-CoV-2 among children in the Philippines.

Four endemic human coronaviruses (HCoV), HCoV-229E, HCoV-NL63, HCoV-HKU1, and HCoV-OC43, are closely related to SARS-CoV-2. These coronaviruses are known to infect humans living in temperate areas, including children under 5 years old; however, the seroprevalence of four HCoVs among children in tropical areas, including the Philippines, remains unclear. This study aimed to assess the prevalence of antibodies against four HCoVs and to determine the reactivity and neutralization of these antibodies against SARS-CoV-2 among children in the Philippines. A total of 315 serum samples collected from 2015 to 2018, before the emergence of SARS-CoV-2, in Biliran island, Philippines, were tested for the presence of antibodies against four HCoVs and SARS-CoV-2 using recombinant spike ectodomain proteins by IgG-enzyme-linked immunosorbent assay (ELISA). Reactivity to and neutralization of SARS-CoV-2 were also investigated. The seroprevalence of the four HCoVs was 63.8% for HCoV-229E, 71.4% for HCoV-NL63, 76.5% for HCoV-HKU1, and 83.5% for HCoV-OC43 by ELISA. Age group analysis indicated that seropositivity to all HCoVs reached 80% by 2-3 years of age. While 69/315 (21.9%) of the samples showed reactive to SARS-CoV-2, almost no neutralization against SARS-CoV-2 was detected using neutralization assay. Reactivity of antibodies against SARS-CoV-2 spike protein obtained by ELISA may not correlate with neutralization capability.

SARS-CoV-2 seroprevalence among children in Latvia: A cross-sectional study.

Coronavirus disease 2019 (COVID-19) is a major global health concern. In contrast to adults, the course of the disease has been observed to be mild or even asymptomatic in children. It is therefore both clinically and epidemiologically important to measure the seroprevalence in children and adolescents to discern the overall morbidity of the disease and to compare these findings with similar data collected globally. We conducted a cross-sectional study between March and July of 2022 at the Children Clinical University Hospital in Riga, Latvia, to evaluate the seroprevalence of antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Participants aged 0 to 18 years were enrolled during hospitalization for reasons other than COVID-19. The levels of SARS-CoV-2 spike protein and nucleocapsid antibodies were measured in blood samples. The possibility of transplacental antibody transport was evaluated by directly interviewing the mothers of participants aged 18 months and younger. Various demographic and epidemiological risk factors and their association with seroprevalence were analyzed. Positive SARS-CoV-2 nucleocapsid antibodies were designated the main criterion for seropositivity. Of 200 enrolled children, 173 were found to be seropositive, resulting in an overall seroprevalence of 86.5%. The highest seroprevalence was detected in children and adolescents aged 12 to 18 years. With the progression of the COVID-19 pandemic, the seroprevalence in children has increased significantly. We found that almost 1-third of seropositive children in our study population were unaware of being previously infected with SARS-CoV-2 due to an asymptomatic course of the disease. Our study findings pertaining to high seropositivity among children and adolescents might be beneficial for public authorities to adapt epidemiological strategies and prevention measures. The high seroprevalence rate reported here and in many other populations around the world suggests that COVID-19 will likely become one of the many seasonal viral infections.

Age-specific contribution of contacts to transmission of SARS-CoV-2 in Germany.

Current estimates of pandemic SARS-CoV-2 spread in Germany using infectious disease models often do not use age-specific infection parameters and are not always based on age-specific contact matrices of the population. They also do usually not include setting- or pandemic phase-based information from epidemiological studies of reported cases and do not account for age-specific underdetection of reported cases. Here, we report likely pandemic spread using an age-structured model to understand the age- and setting-specific contribution of contacts to transmission during different phases of the COVID-19 pandemic in Germany. We developed a deterministic SEIRS model using a pre-pandemic contact matrix. The model was optimized to fit age-specific SARS-CoV-2 incidences reported by the German National Public Health Institute (Robert Koch Institute), includes information on setting-specific reported cases in schools and integrates age- and pandemic period-specific parameters for underdetection of reported cases deduced from a large population-based seroprevalence studies. Taking age-specific underreporting into account, younger adults and teenagers were identified in the modeling study as relevant contributors to infections during the first three pandemic waves in Germany. For the fifth wave, the Delta to Omicron transition, only age-specific parametrization reproduces the observed relative and absolute increase in pediatric hospitalizations in Germany. Taking into account age-specific underdetection did not change considerably how much contacts in schools contributed to the total burden of infection in the population (up to 12% with open schools under hygiene measures in the third wave). Accounting for the pandemic phase and age-specific underreporting is important to correctly identify those groups of the population in which quarantine, testing, vaccination, and contact-reduction measures are likely to be most effective and efficient. Age-specific parametrization is also highly relevant to generate informative age-specific output for decision makers and resource planers.

Quantifying the effect of delaying the second COVID-19 vaccine dose in England: a mathematical modelling study.

BACKGROUND: The UK was the first country to start national COVID-19 vaccination programmes, initially administering doses 3 weeks apart. However, early evidence of high vaccine effectiveness after the first dose and the emergence of the SARS-CoV-2 alpha variant prompted the UK to extend the interval between doses to 12 weeks. In this study, we aimed to quantify the effect of delaying the second vaccine dose in England. METHODS: We used a previously described model of SARS-CoV-2 transmission, calibrated to COVID-19 surveillance data from England, including hospital admissions, hospital occupancy, seroprevalence data, and population-level PCR testing data, using a Bayesian evidence-synthesis framework. We modelled and compared the epidemic trajectory in the counterfactual scenario in which vaccine doses were administered 3 weeks apart against the real reported vaccine roll-out schedule of 12 weeks. We estimated and compared the resulting numbers of daily infections, hospital admissions, and deaths. In sensitivity analyses, we investigated scenarios spanning a range of vaccine effectiveness and waning assumptions. FINDINGS: In the period from Dec 8, 2020, to Sept 13, 2021, the number of individuals who received a first vaccine dose was higher under the 12-week strategy than the 3-week strategy. For this period, we estimated that delaying the interval between the first and second COVID-19 vaccine doses from 3 to 12 weeks averted a median (calculated as the median of the posterior sample) of 58 000 COVID-19 hospital admissions (291 000 cumulative hospitalisations [95% credible interval 275 000-319 000] under the 3-week strategy vs 233 000 [229 000-238 000] under the 12-week strategy) and 10 100 deaths (64 800 deaths [60 200-68 900] vs 54 700 [52 800-55 600]). Similarly, we estimated that the 3-week strategy would have resulted in more infections compared with the 12-week strategy. Across all sensitivity analyses the 3-week strategy resulted in a greater number of hospital admissions. In results by age group, the 12-week strategy led to more hospitalisations and deaths in older people in spring 2021, but fewer following the emergence of the delta variant during summer 2021. INTERPRETATION: England's delayed-second-dose vaccination strategy was informed by early real-world data on vaccine effectiveness in the context of limited vaccine supplies in a growing epidemic. Our study shows that rapidly providing partial (single-dose) vaccine-induced protection to a larger proportion of the population was successful in reducing the burden of COVID-19 hospitalisations and deaths overall. FUNDING: UK National Institute for Health Research; UK Medical Research Council; Community Jameel; Wellcome Trust; UK Foreign, Commonwealth and Development Office; Australian National Health and Medical Research Council; and EU.

Escalating spread of SARS-CoV-2 infection after school reopening among students in hotspot districts of Oromia Region in Ethiopia: Longitudinal study.

BACKGROUND: COVID-19 pandemic caused by extended variants of SARS-CoV-2 has infected more than 350 million people, resulting in over 5.5 million deaths globally. However, the actual burden of the pandemic in Africa, particularly among children, remains largely unknown. We aimed to assess the seroepidemiological changes of SARS-CoV-2 infection after school reopening among school children in Oromia, Ethiopia. METHODS: A prospective cohort study involving students aged 10 years and older were used. A serological survey was performed twice, at school reopening in December 2020 and four months later in April 2021. Participants were selected from 60 schools located in 15 COVID-19 hotspot districts in Oromia Region. Serology tests were performed by Elecsys anti-SARS-CoV-2 nucleocapsid assay. Data were collected using CSentry CSProData Entry 7.2.1 and exported to STATA version 14.2 for data cleaning and analysis. RESULTS: A total of 1884 students were recruited at baseline, and 1271 completed the follow-up. SARS-CoV-2 seroprevalence almost doubled in four months from 25.7% at baseline to 46.3% in the second round, with a corresponding seroincidence of 1910 per 100,000 person-week. Seroincidence was found to be higher among secondary school students (grade 9-12) compared to primary school students (grade 4-8) (RR = 1.6, 95% CI 1.21-2.22) and among those with large family size (> = 5) than those with a family size of <3 (RR = 2.1, 95% CI 1.09-4.17). The increase in SARS-CoV-2 seroprevalence among the students corresponded with Ethiopia's second wave of the COVID-19 outbreak. CONCLUSION: SARS-CoV-2 seroprevalence among students in hotspot districts of the Oromia Region was high even at baseline and almost doubled within four months of school recommencement. The high seroincidence coincided with the second wave of the COVID-19 outbreak in Ethiopia, indicating a possible contribution to school opening for the new outbreak wave.

Seroepidemiology of SARS-CoV-2 on a partially vaccinated island in Brazil: Determinants of infection and vaccine response.

Background: A vaccination campaign targeted adults in response to the pandemic in the City of Rio de Janeiro. Objective: We aimed to evaluate the seroprevalence of SARS-CoV-2 antibodies and identify factors associated with seropositivity on vaccinated and unvaccinated residents. Methods: We performed a seroepidemiologic survey in all residents of Paquetá Island, a neighborhood of Rio de Janeiro city, during the COVID-19 vaccine roll-out. Serological tests were performed from June 16 to June 19, 2021, and adjusted seropositivity rates were estimated by age and epidemiological variables. Logistic regression models were used to estimate adjusted ORs for risk factors to SARS-CoV-2 seropositivity in non-vaccinated individuals, and potential determinants of the magnitude of antibody responses in the seropositive population. Results: We included in the study 3,016 residents of Paquetá (83.5% of the island population). The crude seroprevalence of COVID-19 antibodies in our sample was 53.6% (95% CI = 51.0, 56.3). The risk factors for SARS-CoV-2 seropositivity in non-vaccinated individuals were history of confirmed previous COVID-19 infection (OR = 4.74; 95% CI = 3.3, 7.0), being a household contact of a case (OR = 1.93; 95% CI = 1.5, 2.6) and in-person learning (OR = 2.01; 95% CI = 1.4, 3.0). Potential determinants of the magnitude of antibody responses among the seropositive were hybrid immunity, the type of vaccine received, and time since the last vaccine dose. Being vaccinated with Pfizer or AstraZeneca (Beta = 2.2; 95% CI = 1.8, 2.6) determined higher antibody titers than those observed with CoronaVac (Beta = 1.2; 95% CI = 0.9, 1.5). Conclusions: Our study highlights the impact of vaccination on COVID-19 collective immunity even in a highly affected population, showing the difference in antibody titers achieved with different vaccines and how they wane with time, reinforcing how these factors should be considered when estimating effectiveness of a vaccination program at any given time. We also found that hybrid immunity was superior to both infection-induced and vaccine-induced immunity alone, and online learning protected students from COVID-19 exposure.

SARS-CoV-2 infection prevalence and associated factors: a serial population-based study in Espírito Santo, Brazil, May to June 2020. / Prevalência e fatores associados à infecção por SARS-CoV-2: estudo de base populacional seriado, no Espírito Santo, de maio a junho/2020.

OBJECTIVE: To analyze SARS-CoV-2 seroprevalence and association of sociodemographic and clinical aspects in the state of Espírito Santo, Brazil. METHODS: This was a serial cross-sectional study carried out in four phases, using households as the unit of analysis, from May to June 2020. Eleven municipalities were surveyed, with a sample of 4,500 households in each phase. RESULTS: Prevalence ranged from 2.1% (95%CI 1.7;2.5) on May 10 (first phase) to 9.6% (95%CI 8.8;10.4) on June 21 (fourth phase). In the Greater Vitória Metropolitan Region, the prevalence were 2.7% (95%CI 2.2;3.3) in the first phase, and 11.5% (95%CI 10.5;12.6) in the fourth phase; in the interior region of the state, prevalence ranged from 0.4% (95%CI 0.1;0.9) to 4.4% (95%CI 3.2;5.5) between the two phases. CONCLUSION: The increase in SARS-CoV-2 seroprevalence found in the fourth phase highlighted the high transmission of the virus, information that can support management of the pandemic.

Seroprevalence of Covid-19 infection among healthcare workers: A study from a tertiary care hospital in the National Capital Region of India.

Background Seroprevalence studies on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can provide information on the target populations for vaccination. We aimed to evaluate the seroprevalence among healthcare workers (HCWs) at our tertiary care institution and to identify parameters that may affect it. Method We assessed seroprevalence of SARS-CoV-2 by the chemiluminescence immunoassay test among 3258 HCW in our hospital and evaluated as per gender, age, their previous Covid-19 diagnosis, role in hospital and type/risk of exposure. Results Of 3258 participants, 46.2% (95% CI 44.4%- 47.9%) were positive for SARS-CoV-2 IgG antibodies (i.e. IgG ≥15 AU/ml). Higher seroprevalence was seen in non-clinical HCWs (50.2%) than in clinical HCWs (41.4%, p=0.0001). Furthermore, people with a history of Covid-19 were found to have significantly higher antibody levels (p=0.0001). Among the HCWs, doctors and nurses had lower relative risk (RR) of acquiring Covid-19 infection (RR=0.82; 95% CI 0.76-0.89) compared to non-clinical HCWs. Conclusion Seroprevalence in HCWs at our hospital was 46.2%. Clinical HCWs had lower seroprevalence compared to non-clinical HCWs. Previous history of Covid-19 almost doubled the seropositivity, particularly in those with current infection.

Seroprevalence of Specific SARS-CoV-2 Antibodies during Omicron BA.5 Wave, Portugal, April-June 2022.

After the rapid spread of SARS-CoV-2 BA.5 Omicron lineage in Portugal, we developed a seroepidemiologic survey based on a sample of 3,825 residents. Results indicated that from April 27 through June 8, 2022, the estimated seroprevalence of SARS-CoV-2 nucleocapsid or spike IgG was 95.8%, which indicates a high level of protection.