Abstract
<title>Abstract</title> <p>Background Passive surveillance of adverse events following immunization (AEFI) and active surveillance of adverse events of special interest (AESI) were implemented during the introduction of novel oral poliovirus vaccine type 2 (nOPV2) in the Central African Republic (CAR). This study aimed to describe the epidemiological and clinical characteristics of AEFIs reported during the introduction of nOPV2 and to assess vaccine safety through passive and active surveillance systems. Methods We conducted a retrospective analytical study covering the period from 3 June to 30 October 2022. Sociodemographic, clinical, and vaccination-related data were collected through the Open Data Kit (ODK) platform. Statistical analyses were performed using STATA version 16.1. Bivariate and multivariable logistic regression analyses were conducted to identify factors associated with serious AEFIs. Results A total of 2,997,902 doses of nOPV2 were administered during two vaccination rounds. Overall, 424 AEFIs were reported, corresponding to a reporting rate of 14.1 AEFIs per 100,000 administered doses. Fever was the most frequently reported clinical manifestation (42.4%), followed by diarrhoea and vomiting. Out the 48 serious AEFIs reported, 45 were investigated and 35 underwent causality assessment. Among the assessed cases, 11 (31.4%) were classified as vaccine product-related reactions. Out of 184 line-listed, 92 confirmed AESI in the 7 sentinel sites with 62 anaphylaxis, 29 meningitis and 1 unexplained death. Conclusions The introduction of nOPV2 in the Central African Republic demonstrated a favourable safety profile based on both passive AEFI surveillance and active AESI surveillance. Strengthening pharmacovigilance activities, improving data completeness, and enhancing investigation capacities remain essential for generating robust vaccine safety evidence and maintaining public confidence in immunization programmes.</p>