Predictors of seropositivity against SARS-COV-2: a population-based seroepidemiological study

Abstract Background Data on parameters of actual exposure to SARS-CoV-2 is limited, and specific population groups might be at a higher risk of infection. In line with the growing need for large-scale investigations to determine the presence of antibodies against SARS-CoV-2 among different population groups, we conducted a nationwide assessment in Armenia. Methods We performed a cross-sectional seroepidemiological study among the adult population in Armenia, in May-September 2021. A multi-stage cluster random sampling was performed to recruit the participants across the capital city and regions. The study had two main components: blood sampling, which took place in primary care facilities and a phone survey on socio-demographic characteristics, comorbidities, and previous history of COVID-19. Results The number of participants included in both blood sampling and phone survey was 3483. The nationwide prevalence of SARS-CoV 2 antibodies weighted by age and gender was 66.4% with significantly higher prevalence in urban compared to rural areas (67.3% vs 59.3%, p < 0.001). Only 22.7% (n = 772) of the total sample reported a previous history of PCR confirmed COVID-19, among whom antibodies were detected in 94.2% (n = 727). In the final adjusted model, the seropositivity was associated with being female (OR = 1.60, 95% CI: 1.32; 1.92), employed (OR = 1.41, 95% CI: 1.17; 1.69), and having previous PCR confirmed COVID-19 (OR = 10.6, 95% CI: 7.39; 15.21). Conclusions Over 66% of the population were seropositive for antibodies against SARS-CoV 2; and over ⅕ of the sample reported a previous PCR diagnosis. Factors associated with increased odds of seropositivity included gender, employment status, and place of residence. Targeted interventions are recommended to minimize the risk of infection among those groups, including vaccination and infection prevention and control measures. Key messages • The prevalence of SARS-CoV 2 antibodies is about three times higher than the rate of infection based on PCR confirmed prevalence of COVID-19. • Women, people living in urban areas, and those employed are at a higher risk for exposure to SARS-CoV 2.


Background:
In 2020, the study ''Corona-Monitoring Lokal'' (CoMoLo) assessed seroprevalences of SARS-CoV-2 IgG antibodies in four study locations that were particularly affected by outbreaks in the early stages of the pandemic in Germany. One of the objectives of the 2021 follow-up was to examine the development of immunological parameters over time, including the extent of IgG antibody waning after vaccination. Methods: Venous blood specimens were collected from a sample of initial study participants over a 2-week period between May and October 2021, with an oversampling of seropositive or previously infected individuals. Levels of IgG antibodies to the SARS-CoV-2 spike protein were measured from serum using Anti-SARS-CoV-2-QuantiVac-ELISA (IgG) tests by Euroimmun. Information on SARS-CoV-2 vaccinations or known infections was collected via online questionnaires or telephone interviews.

Results:
A total of 3328 participants (74% response) gave blood specimens for this follow-up study, with questionnaire information available for 2843 (85%) of these. Preliminary analyses suggest that in participants who had received two doses of a vaccine more than 3 weeks before giving blood (n = 1583), IgG levels decreased exponentially by about 9.8% (95%CI 9.1% -10.4%) with each additional week since the last dose, when controlling for age, sex, and type of vaccine. There was evidence of this waning effect differing by vaccine type. Antibody levels also appear to decline with increasing age, according to preliminary results. Final results of the linear model used to assess the dynamics and predictive factors of antibody levels will be reported.

Conclusions:
This follow-up study will add evidence to an improved understanding of antibody waning after SARS-CoV-2 vaccination. Preliminary results are in line with international studies and may be helpful for discussions on potential benefits of further vaccinations in Germany.

Key messages:
Antibodies induced by COVID-19 vaccination wane over time. The magnitude of this effect differs by vaccine type. Antibodies also decreased with increasing age. Our results may be helpful for discussions on potential benefits of further COVID-19 vaccinations in Germany.

Background:
Data on parameters of actual exposure to SARS-CoV-2 is limited, and specific population groups might be at a higher risk of infection. In line with the growing need for large-scale investigations to determine the presence of antibodies against SARS-CoV-2 among different population groups, we conducted a nationwide assessment in Armenia.

Methods:
We performed a cross-sectional seroepidemiological study among the adult population in Armenia, in May-September 2021. A multi-stage cluster random sampling was performed to recruit the participants across the capital city and regions. The study had two main components: blood sampling, which took place in primary care facilities and a phone survey on sociodemographic characteristics, comorbidities, and previous history of COVID-19.

Results:
The number of participants included in both blood sampling and phone survey was 3483. The nationwide prevalence of SARS-CoV 2 antibodies weighted by age and gender was 66.4% with significantly higher prevalence in urban compared to rural areas (

Conclusions:
Over 66% of the population were seropositive for antibodies against SARS-CoV 2; and over 1=5 of the sample reported a previous PCR diagnosis. Factors associated with increased odds of seropositivity included gender, employment status, and place of residence. Targeted interventions are recommended to minimize the risk of infection among those groups, including vaccination and infection prevention and control measures.

Key messages:
The prevalence of SARS-CoV 2 antibodies is about three times higher than the rate of infection based on PCR confirmed prevalence of COVID-19. Women, people living in urban areas, and those employed are at a higher risk for exposure to SARS-CoV 2.
1.N. Oral presentations: Child and adolescent public health