Adverse events following vaccination in northern Iran

Adverse events following immunization (AEFI) are unfavorable or unintended signs, symptoms, diseases or abnormal laboratory findings which usually occur within 28 days following vaccination. This study aimed to analyze the ratio and patterns of AEFIs reported from all vaccination centers affiliated to Babol University of Medical Sciences, north of Iran. This study was carried out as a cross-sectional research using the vaccine safety surveillance databank related to all individuals who were vaccinated at Babol University of Medical Sciences, during eight years (from 2014 to 2021), and had at least one adverse event following immunization. All patients were included by census. Given the most probable factor caused the occurrence of adverse events, AEFI was categorized as following: 1- vaccine reaction; 2- injection reaction; 3- immunization error related reaction; 4- coincidental event; 5- unknown cause. Data was analyzed using SPSS 22 software package. P-value ≤ 0.05 was considered as the significant level. A total of 934 individuals reported AEFI. The average reporting ratio of adverse events was 5.67 per 10,000 vaccine doses administered. The highest rate of adverse events was attributed to coronavirus vaccine (28.1%), pentavalent (21.0%), and DTP (Diphtheria, Tetanus and Pertussis) (20.3%), respectively. The most common signs or symptoms were mild local adverse reactions (30.1%) and mild fever (24.1%). In final classification, 94.0% of AEFI were vaccine reactions, followed by injection reaction (3.1%). Although a downward trend of AEFI was observed over the 8-year period, the incidence rate of adverse events following immunization needs more attention.