Impact of international travels on seroprevalence of SARS-CoV-2 among residents of Chelyabinsk city

SARS-CoV-2 seroprevalence is an important index of coronavirus infection incidence, especially among populations with different mobility levels. International travel may facilitate transmission of the virus and affect the level of herd immunity, but the extent of this influence remains poorly understood. The present study was conducted in Chelyabinsk from 27.10.2020 to 30.01.2023. 660 blood samples were analyzed for IgM antibodies, and 843 samples for IgG antibodies to SARS-CoV-2 antigen in order to assess seropositivity rates of city residents depending on their recent international travel experience. Antibodies to coronavirus infection were determined by enzyme-linked immunosorbent assay (ELISA) using Multiskan FC equipment and Vector-Best reagents. A questionnaire filled by the participants helped to establish the fact of travel and the countries visited. The results of this study showed a trend towards higher IgG seropositivity among individuals who had traveled internationally (p = 0.07), although statistical significance was not reached. The overall seroprevalence rate was higher for IgG (67.38%) compared to IgM (32.73%), thus, probably, suggesting a history of infection or vaccination in the cohort. The highest IgG seroprevalence was observed among persons who returned from Turkey, Kazakhstan, and Egypt. No statistically significant differences in seroprevalence were found between men and women. The results suggest a trend towards higher seroprevalence among the international travelers, thus being indicative for increased risk of infection during the trips. However, a lack of statistical significance requires further surveys in larger groups, as well as considering their vaccination status, seroconversion dynamics, disease time profile, and repeated testing. Despite these limitations, these results can be used to improve epidemiological surveillance measures and planning epidemiological measures in order to prevent COVID-19 and other respiratory infections, including the factor of international travelling.