Publication date: Nov 22, 2024

The COVID-19 pandemic has significantly impacted global health, with varying vaccine effectiveness (VE) across different regions and vaccine platforms. In Africa, where vaccination rates are relatively low, inactivated vaccines like BBIP-CorV (Sinopharm) and Coronovac (Sinovac) have been widely used. This study evaluated the real-world effectiveness of licensed inactivated COVID-19 vaccines in Zimbabwe during a period dominated by Omicron variants. We conducted a prospective, test-negative, case-control study among symptomatic adults across six Zimbabwean provinces from November 2022 to October 2023. Participants were categorized based on vaccination status, and nasopharyngeal swabs were collected for SARS-CoV-2 PCR testing. Vaccine effectiveness was assessed using conditional logistic regression, adjusting for various covariates such as age, sex, and comorbidities. Among 5175 participants, 701 tested positive for SARS-CoV-2 and 4474 tested negative. The overall adjusted VE against symptomatic COVID-19 was 31% (95% CI: 5. 3-49. 7%) among verified vaccinated individuals. Boosted individuals demonstrated a higher VE of 59. 8% (95% CI: 40. 3-72. 9%). VE decreased significantly to 24% (95% CI: -4. 1-44. 8%) in individuals vaccinated over a year prior. Similar VE was observed for BBIP-CorV (36. 8%, 95% CI: 11. 4-54. 9%) and Coronovac (38. 1%, 95% CI: 16. 3-54. 2%). This study indicates modest protection from inactivated COVID-19 vaccines against symptomatic Omicron infection, with significant enhancement following booster doses. These findings highlight the need for continued vaccine evaluation, particularly in resource-limited settings, to inform public health strategies and optimize vaccination programs.

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