The Real-World Effectiveness of Inactivated COVID-19 Vaccines in Zimbabwe During the Omicron Variant Dominance: A Test-Negative Case-Control Study.

Background/objectives: 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.

Methods: 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.

Results: 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%).

Conclusions: 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.