Herd immunity to hepatitis A virus in the Saint Petersburg and Leningrad Region

In 2023, 3,545 cases of viral hepatitis A (HA) were reported in the Russian Federation, with an incidence rate of 2.42 per 100,000 population. Acute HA accounted for the largest share in the structure of acute viral hepatitis morbidity – 61%, and in comparison, with 2010, its specific weight increased 1.3 times (55% – in 2010). Currently, there is no specific treatment for HA. Vaccination remains the most effective method to eliminate viral hepatitis A in the population. In 2023, 423,855 people were vaccinated in the country, including 171,161 children up to and including 17 years of age. The aim of our work was to assess the seroprevalence of IgG antibodies to hepatitis A virus in the population of St. Petersburg and Leningrad Region depending on the infection-vaccine status and socio-demographic characteristics. In a population-based study, 6773 volunteers from St. Petersburg and Leningrad Region aged 1 year to 70+ years were examined. Volunteers were stratified into 9 age groups: 1-5 years (n = 370), 6-11 years (n = 511), 12-17 years (n = 538), 18-29 years (n = 792), 30-39 years (n = 838), 40-49 years (n = 914), 50-59 years (n = 900), 69-69 years (n = 930), and 70+ years (n = 980). ELISA testing was performed using reagent kits manufactured by Vector-Best (Russia) according to manufacturer instructions: “Vectohep A-IgG” for the presence of antibodies to hepatitis A virus. In the course of the study, anti-HAV IgG antibodies were detected in 38.1% of people. A direct correlation between the frequency of anti-HAV IgG antibodies and increasing age was shown. High frequency of anti-HAV IgG antibodies was found among workers in the scientific, transport and medical spheres. The lowest frequency of anti-HAV IgG antibodies was found among office and IT workers, and civil servants. The proportion of vaccinated persons in St. Petersburg was significantly lower than in Leningrad Region. Among unvaccinated volunteers from St. Petersburg and Leningrad Region, anti-HAV IgG antibodies were detected in 37.3% of people; however, those examined were sure that they had never had HA. The proportion of vaccinated persons among educational and medical workers was 10.1% and 12.0%, respectively. It should be noted that these groups are among the risk groups for whom vaccination against HAV is recommended.It is shown that residents of St. Petersburg and the Leningrad Region continue to be in contact with HAV, and risk groups are not sufficiently covered by vaccination. Given the increasing seroprevalence of anti-HAV IgG antibodies with age, the issue of HA prophylaxis remains highly relevant.The study of herd immunity to HAV in different regions to obtain a more reliable picture of the pathogen distribution in the Russian Federation, as well as to identify hidden foci, will further improve the effectiveness of specific immunisation.