Characteristics and factors of repeated influenza vaccination among elderly individuals in Shanghai, China from 2020 to 2022.

Elderly individuals face a high risk of hospitalization and death related to influenza, thus prioritizing them for influenza vaccination. Due to variations in the influenza virus and waning protective antibodies, annual influenza vaccination is recommended. However, research on repeated influenza vaccination among elderly individuals in China is limited. From 2020 to 2022, the average influenza vaccination coverage among registered elderly individuals in Shanghai was 4.1%, showing a declining trend over time. In 2020, the rate of repeated influenza vaccination among elderly individuals was 28.35%, which rose to almost two-thirds both in 2021 and 2022. No increased risk of adverse events following immunization was observed after repeated influenza vaccination during this period. Our study also found that elderly individuals with Shanghai household registration, managed by community clinics, and older age tended to receive more doses of repeated influenza vaccination throughout the period from 2020 to 2022. Increasing influenza vaccine coverage among elderly individuals in Shanghai is both urgent and challenging. Health authorities should intensify educational and promotional campaigns to encourage uptake of annual repeated influenza vaccination among elderly individuals.