BackgroundLongitudinal surveys to continually monitor the seroprevalence around the globe are required to support the prevention and control efforts for assessment of the levels of endemic stability in certain countries and regions. We investigated seroprevalence of anti-SARS-CoV-2-S1 receptor-binding domain (RBD)–specific antibodies in the samples of participants recruited for various cardiovascular studies unrelated to exposure to the virus in 2011-2021. A cohort study recruited in 2019-2021 was used to evaluate the vaccination and anti-IgG-SARS-CoV-2–S1 RBD-positive statuses to assess the resistance and severity of Covid-19. Materials and MethodsThe present observational study included subjects 18 years of age and older randomly selected from various cohorts previously recruited from 2011 to 2021 from the city of Moscow and Moscow Region for a total of 565 serum samples including recent participants (N = 310); recruited in 2019-2021. The phone survey of the participants of this cohort was conducted in October, 2021. Anti-SARS-CoV-2 S1 RBD-specific antibodies were assayed in the serum samples (N = 565). At endpoint (October 30, 2021), participants of the 2019-2021 cohort (N = 310) were interviewed over phone using a questionnaire that included 5 questions as follows: 1) did the participant experience a respiratory disorder at any time before or after the enrolment in the study; 2) the date of the disorder; 3) severity of the disorder, including asymptomatic, mild, medium (fever and cough), or severe (hospitalization); 4) was the participant vaccinated and the date of vaccination; and 5) brand of a vaccine. ResultsThe data of the present study indicated that a small percentage (3-6%) of SARS-CoV-2-S1 RBD-specific antibodies was detected in participants recruited in 2011-2019. The percentage of SARS-CoV-2-S1 RBD-specific antibodies was increased to 16.5% in 2020 and to 46% in 2021. The vaccination rate of 238 respondents of this cohort was 58% from August, 2020 to October, 2021. If this rate is added to the rate of not vaccinated SARS-CoV-2-S1 RBD-positive subjects (11%), collective immunity was able to reach 69%. The data indicated that 12% of respondents were hospitalized. No cases of hospitalization were reported in vaccinated respondents. The morbidity rate in the subgroup of anti-SARS-CoV-2-S1 RBD-positive respondents was 5.4-fold higher than that in the subgroup of vaccinated respondents (OR = 5.4; CI: 1.4 -19.8; P = 0.01).ConclusionDetected small percentage of SARS-CoV-2-S1 RBD-specific antibodies in participants recruited in 2011-2019 indicated possible spreading of coronaviruses during the pre-pandemic period. Collective immunity in Moscow and Moscow region was able to reach 69% from August, 2020 to October, 2021. Obtained results demonstrated that vaccination protects against COVID-19 and related hospitalization
