Adverse events following immunization during COVID-19 mass vaccination campaigns in the Democratic Republic of Congo: Findings from active safety surveillance

Introduction: Post-marketing safety surveillance is indispensable for ensuring safety and public trust in vaccines, particularly in African settings where evidence of COVID–19 vaccine safety is less documented. We aimed to identify the types of adverse events following immunization (AEFIs), the overall incidence, and factors associated with AEFIs during mass vaccination campaigns in The Democratic Republic of Congo (DRC). Methods: From December 1 to 29, 2023, a prospective safety surveillance study was conducted on 4,766 individuals in Kinshasa Province in DRC. They were surveyed through phone calls from day 1 to 28 following the administration of the COVID-19 vaccine. We calculated AEFI incidence rates by type of vaccine, sex, and age group. We identified factors associated with AEFIs using multivariable logistic regression models, which were expressed by adjusted odds ratio (aOR) and its 95% confidence interval (CI). Results: A total of 4766 participants were included in the study. The median age of the participants was 36 years, with an interquartile range of 27 to 48 years and 2503 (53%) were females. Most of the participants (94.6%) received the Johnson & Johnson (J&J) vaccine, while 256 (5.4%) received the Pfizer vaccine. Nearly a quarter of participants (23.75%, 95% CI: 22.54%-24.99%) reported AEFIs. The most common AEFIs reported were fever (9.61%, 95%CI: 8.88%-10.48%), injection site pain (9.00%, 95%CI: 8.20%-9.85%), headache (4.11%, 95%CI: 3.57%-4.72%), stiffness (1.51%, 95%CI: 1.18%-1.89 %) and myalgia (1.15%, 95%CI: 0.87%-1.49%). The incidence of AEFIs was higher for the Pfizer vaccine at 34.48% (95% CI: 28.57%-40.54%) compared to 23.15% (95% CI: 21.92%-24.41%) for the J&J vaccine. Participants aged 36 years and above were associated with increased odds of reporting any adverse event (aOR=1.17, 95%CI: 1.02-1.33), injection site pain (aOR=1.36, 95% CI: 1.11-1.66), and two or more signs (aOR=1.46, 95%CI: 1.10-1.94), compared to those below 36 years of age. Conclusions: AEFI reported by about a quarter of participants and its association with vaccine type and older age underscores the need for systematic vaccine safety monitoring in the population. This is critical for developing future vaccination strategies tailored to individuals more susceptible to AEFIs.