ABSTRACT
BackgroundThe COVID-19 pandemic in Russia has already resulted in 500,000 excess deaths, with more than 5.6 million cases registered officially by July 2021. Surveillance based on case reporting has become the core pandemic monitoring method in the country and globally. However, population-based seroprevalence studies may provide an unbiased estimate of the actual disease spread and, in combination with multiple surveillance tools, help to define the pandemic course. This study summarises results from four consecutive serological surveys conducted between May 2020 and April 2021 at St. Petersburg, Russia and combines them with other SARS-CoV-2 surveillance data. MethodsWe conducted four serological surveys of two random samples (May-June, July-August, October-December 2020, and February-April 2021) from adults residing in St. Petersburg recruited with the random digit dialing (RDD), accompanied by a telephone interview to collect information on both individuals who accepted and declined the invitation for testing and account for non-response. We have used enzyme-linked immunosorbent assay CoronaPass total antibodies test (Genetico, Moscow, Russia) to report seroprevalence. We corrected the estimates for non-response using the bivariate probit model and also accounted the test performance characteristics, obtained from independent assay evaluation. In addition, we have summarised the official registered cases statistics, the number of hospitalised patients, the number of COVID-19 deaths, excess deaths, tests performed, data from the ongoing SARS-CoV-2 variants of concern (VOC) surveillance, the vaccination uptake, and St. Petersburg search and mobility trends. The infection fatality ratios (IFR) have been calculated using the Bayesian evidence synthesis model. FindingsAfter calling 113,017 random mobile phones we have reached 14,118 individuals who responded to computer-assisted telephone interviewing (CATI) and 2,413 provided blood samples at least once through the seroprevalence study. The adjusted seroprevalence in May-June, 2020 was 9.7% (95%: 7.7-11.7), 13.3% (95% 9.9-16.6) in July-August, 2020, 22.9% (95%: 20.3-25.5) in October-December, 2021 and 43.9% (95%: 39.7-48.0) in February-April, 2021. History of any symptoms, history of COVID-19 tests, and non-smoking status were significant predictors for higher seroprevalence. Most individuals remained seropositive with a maximum 10 months follow-up. 92.7% (95% CI 87.9-95.7) of participants who have reported at least one vaccine dose were seropositive. Hospitalisation and COVID-19 death statistics and search terms trends reflected the pandemic course better than the official case count, especially during the spring 2020. SARS-CoV-2 circulation showed rather low genetic SARS-CoV-2 lineages diversity that increased in the spring 2021. Local VOC (AT.1) was spreading till April 2021, but B.1.617.2 substituted all other lineages by June 2021. The IFR based on the excess deaths was equal to 1.04 (95% CI 0.80-1.31) for the adult population and 0.86% (95% CI 0.66-1.08) for the entire population. ConclusionApproximately one year after the COVID-19 pandemic about 45% of St. Petersburg, Russia residents contracted the SARS-CoV-2 infection. Combined with vaccination uptake of about 10% it was enough to slow the pandemic until the Delta VOC started to spread. Combination of several surveillance tools provides a comprehensive pandemic picture. FundingPolymetal International plc.
ABSTRACT
BackgroundEstimates from initial SARS-CoV-2 serological surveys were likely to be biased due to convenience sampling whereas large-scale population-based serosurveys could be biased due to non-response. This study aims to estimate the seroprevalence of SARS-CoV-2 infection in Saint Petersburg, Russia accounting for non-response bias. MethodsWe recruited a random sample of adults residing in St. Petersburg with random digit dialling. Computer-assisted telephone interview was followed by an invitation for an antibody test with randomized rewards for participation. Blood samples collected between May 27, 2020 and June 26, 2020 were assessed for anti-SARS-CoV-2 antibodies using two tests -- CMIA and ELISA. The seroprevalence estimates were corrected for non-response bias, test sensitivity, and specificity. Individual characteristics associated with seropositivity were assessed. Findings66,250 individuals were contacted, 6,440 adults agreed to be interviewed and were invited to participate in the serosurvey. Blood samples were obtained from 1038 participants. Naive seroprevalence corrected for test characteristics was 9.0% [95% CI 7.2-10.8] by CMIA and 10.8% [8.8-12.7] by ELISA. Correction for non-response bias decreased seroprevalence estimates to 7.4% [5.7-9.2] for CMIA and to 9.3% [7.4-11.2] for ELISA. The most pronounced decrease in non-response bias-corrected seroprevalence was attributed to the history of any illnesses in the past 3 months and COVID-19 testing. Besides that seroconversion was negatively associated with smoking status, self-reported history of allergies and changes in hand-washing habits. InterpretationThese results suggest that even low estimates of seroprevalence in Europes fourth-largest city can be an overestimation in the presence of non-response bias. Serosurvey design should attempt to identify characteristics that are associated both with participation and seropositivity. Further population-based studies are required to explain the lower seroprevalence in smokers and participant reporting allergies. FundingPolymetal International plc