Abstract
BACKGROUND: The 2024/25 influenza season in Hungary experienced a major surge in cases, the largest since the COVID-19 pandemic. We evaluated influenza vaccine effectiveness (VE) in primary care settings among adults and vaccination target groups, and also according to time since vaccination, prior seasonal vaccination, and influenza type. METHODS: A test-negative case-control study was conducted in Hungary. Data and specimens were collected from primary care patients with an acute respiratory infection (ARI). Patients with positive PCR test results for influenza were classified as cases, while those with negative test results for influenza were classified as controls. Adjusted VEs were calculated using logistic regression as (1 - odds ratio of vaccination) × 100. RESULTS: Between November 2024 and May 2025, 2074 patients were included in the analysis, of whom 395 cases had influenza. Of the 129 vaccinated patients, 123 (95%) received trivalent inactivated adjuvanted whole-cell vaccine (TIAV), and 6 (5%) received quadrivalent split-virion vaccine. The VE against any influenza was 53% (95% CI: 13-74) in the 18+ age group and 52% (95% CI: 7-75) in the target group for vaccination. The VE against any influenza was 63% (95% CI: 17-84) 14-89 days after vaccination, and 27% (95% CI: -67-68) 90 days or more after vaccination. The VE against any influenza was 56% (95% CI: 1-80) with both current and prior seasonal vaccination, and 5% (95% CI: -64-45) with only prior seasonal vaccination. The VE against influenza A was 39% (95% CI: -16-68), and against influenza B was 80% (95% CI: 2-96). CONCLUSIONS: We observed moderate vaccine effectiveness against any influenza, with higher protection within three months after vaccination. Our research findings provide evidence to inform the development of vaccines and the scheduling of vaccination campaigns, with the aim of maximizing the level of protection provided by vaccines throughout the entire influenza season.