Declining seroprevalence of hepatitis A in Vojvodina, Serbia.

To assess the current hepatitis A virus (HAV) endemicity in the Autonomous Province of Vojvodina, Serbia, we examined the seroprevalence and susceptibility profiles of the general population. A serum bank of 3466 residual samples, collected in 2015-16 as per the specifications of the European Sero-Epidemiology Network 2 project (ESEN2), was tested for anti-HAV antibodies with an enzyme immunoassay. Relationships between anti-HAV positivity and demographic features of respondents were examined by univariable and multivariable analyses. Present-day HAV seroprevalence was compared with that obtained in 1978-79. Surveillance data for hepatitis A recorded between 2008 and 2017 were also analyzed. Age was the only demographic variable found to be independently associated with a HAV seropositive status. Seropositivity (17% overall vs. 79% in 1978-79) increased with age to a maximum of 90% in the elderly ≥60 years. Only 5% of subjects <30 years were seropositive, unlike the 44% of seropositives ≥30 years. The estimated age at midpoint of population immunity (AMPI) increased markedly from 14 years in the late 70s to 55 years in 2015-16. Meanwhile, disease incidence decreased noticeably in recent years (from 11 in 2008 to 2 per 100,000 population in 2017). In the ongoing pre-vaccine era, natural infection provides immunity for merely a third (31%) and two thirds (57%) of people in their 40s and 50s, respectively. Hence, the majority of people ≤40 years (94%) and middle-aged adults 40-49 years (69%) are susceptible to HAV. Older susceptible individuals, particularly those ≥50 years (24%), are prone to severe symptoms. Taken together, these changes reflect the epidemiological transition of Vojvodina and Serbia from high to very low HAV endemicity, thereby supporting the current national policy of immunization of only high-risk groups.