Post-Marketing Active Surveillance of Adverse Events Following Quadrivalent Subunit Influenza Vaccine in Healthy Participants Aged ≥ 3 Years in China

INTRODUCTION: The observational phase IV study through an active surveillance system aimed to assess the safety of the subunit influenza vaccine in healthy individuals aged ≥ 3 years and explore the feasibility of using an active adverse event (AE) surveillance system based on a WeChat Mini Program incorporating electronic diary cards (e-diary cards) in China. METHODS: Between October 30, 2023, and April 28, 2025, a multi-center, open-label, single-arm prospective active surveillance study was conducted. Healthy individuals aged 3 years and above who voluntarily and at their own expense came to the outpatient department to receive the target vaccine (Ab&B Biotech Co., Ltd., Jiangsu, China) were recruited as research participants. The WeChat Mini Program was employed to record baseline information and the occurrence of AEs and adverse drug reactions (ADRs) within 28 days after vaccination. A post hoc subgroup analysis was conducted to assess the safety characteristics of participants in different age groups. RESULTS: Among the 42,881 participants, 495 (11.54‰) reported a total of 682 AEs. No vaccine-related serious adverse events (SAEs) were reported. A total of 293 participants (6.83‰) reported 374 ADRs. Among these, 29 participants (0.68‰) reported 34 unsolicited ADRs, including pharyngalgia (n = 10, 0.23‰) and rhinorrhea (n = 4, 0.09‰) among others. The incidence rates (IR) of AEs across 3-8, 9-17, 18-64, ≥ 65 years groups, from youngest to oldest, were 16.29‰ (n = 269), 10.63‰ (n = 58), 10.53‰ (n = 145), and 3.21‰ (n = 23). A statistically significant difference in AE incidence was observed among the age groups (P < 0.001). CONCLUSIONS: The vaccine demonstrated a favorable safety profile in healthy individuals aged 3 years and above. Moreover, the active surveillance method with the Mini Program was helpful in detecting very rare ADRs. TRIAL REGISTRATION: NCT073326896. Retrospectively registered.