Surveillance of Adverse Events Following Immunization in Children in Mashhad, Iran: A Retrospective Study of Vaccine Safety (2017-2024)

Background Vaccination remains one of the most effective public health measures for preventing infectious diseases. However, adverse events following immunization (AEFIs) can occur, potentially undermining public trust and vaccine acceptance. Effective AEFI surveillance is essential to ensure vaccine safety and optimize immunization programs. This study aimed to assess the incidence, severity, and associated factors of AEFI among children aged seven years and younger in Mashhad, Iran, from 2017–2024. Methods We conducted a retrospective observational study using data from the Sina Electronic Health Record (SINAEHR). AEFI data, including demographic information, vaccination details, and clinical characteristics, were collected from vaccination centers. Adverse events were classified by causality and severity following WHO guidelines. Statistical analyses were performed via IBM SPSS Statistics. Results A total of 13,568 AEFI cases were reported, yielding an incidence rate of 83.38 per 100,000 vaccine doses. Among these reactions, 27.1% were classified as severe reactions. The most common severe AEFIs included lymphadenitis (19.24%) and persistent crying (17.21%). The Pentavalent vaccine was associated with the highest number of AEFI cases (3,614). Statistical analysis revealed a significant association between age and AEFI severity (p = 0.001), as well as between causality and the likelihood of severe reactions (60.6%, p < 0.001). Conclusion This study underscores the importance of continuous AEFI surveillance to safeguard vaccine safety and maintain public confidence in immunization programs. Strengthening monitoring systems, enhancing healthcare provider training, and optimizing vaccine administration protocols are essential for minimizing risks and ensuring effective immunization practices. Future research should prioritize long-term AEFI outcomes and the development of targeted safety interventions for high-risk groups.