Adverse events following immunisation (AEFI) reports from the Zimbabwe expanded programme on immunisation (ZEPI): an analysis of spontaneous reports in Vigibase® from 1997 to 2017

BACKGROUND: Vaccine safety surveillance is an essential requirement in vaccination programmes. It supports signal identification, hypothesis generation, and the identification and rectification of gaps in vaccine pharmacovigilance systems. The objectives of this study were to determine the characteristics and trends of adverse events following immunisation (AEFI) and to assess the performance of the Zimbabwe Expanded Immunisation Programme safety surveillance system. METHODS: We carried out a descriptive study of passively collected vaccine-related Individual Case Safety Report (ICSR) data submitted to the World Health Organization global adverse drug reaction database (VigiBase®) from Zimbabwe during the period 1997 to 2017. We extracted AEFI/ICSR data using VigiLyze® for analysis with respect to the demographic distribution, AEFI characteristics, reporting trends over time, ICSR timeliness and case completeness. RESULTS: A total of 272 vaccine-related ICSRs were included in the analyses with a median completeness score of 0.90 interquartile range, IQR (0.63; 0.90). The overall annual reporting rate was 0.58 per 100,000 vaccine doses and the AEFI reporting ratio ranged between 0 and 30.2 AEFI reports per 100,000 surviving infants. The majority of ICSRs were male (55.3%; p value = 0.641) and the median age was 12 (0–168) months. The majority of ICSRs were reported in children who had received measles (n = 133; 48.9%) and OPV/DTP-Hib-HepB (n = 107; 39.3%) vaccines. Of the 387 observed AEFIs, 301 (77.8%) were systemic events and 86 (22.2%) were local reactions. Systemic events were more frequently reported with doses containing the measles antigen (n = 190; 49.1%) while local events were associated with the multiple antigen OPV/DTP-Hib-HepB (n = 62; 16.0%). The multiple antigen OPV/DTP-Hib-HepB was associated with higher rates for injection site abscess (n = 57), pyrexia (n = 27), diarrhea (n = 15), vomiting (n = 12), and seizures (n = 6). The measles antigen was associated with higher rates for rash (n = 44), ocular disorders (n = 26), pyrexia (n = 26), urticaria (n = 22), diarrhea (n = 8), and vomiting (n = 12). CONCLUSIONS: Most of the ICSRs were associated with measles and OPV/DTP-Hib-HepB vaccines. Zimbabwe’s vaccine safety surveillance system is still developing and is not yet fully functional. However, the current system provides a reference point for the monitoring of the ongoing AEFI reporting trends and characteristics.