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 Sinopharm and Sinovac have been widely used. This study evaluated the real-world effectiveness of licensed inactivated COVID-19 vaccines in Zimba-bwe 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 na-sopharyngeal swabs were collected for SARS-CoV-2 PCR testing. Vaccine effective-ness was assessed using conditional logistic regression, adjusting for various co-variates such as age, sex, and comorbidities. Results: Among 5,175 participants, 701 tested positive for SARS-CoV-2, and 4,474 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 signifi-cantly to 24% (95% CI: -4.1%-44.8%) in individuals vaccinated over a year prior. Similar VE was observed for Sinopharm (36.8%, 95% CI: 11.4%-54.9%) and Sino-vac (38.1%, 95% CI: 16.3%-54.2%). Conclusions: The study indicates modest protection from inactivated COVID-19 vaccines against symptomatic Omicron infection, with significant enhancement fol-lowing booster doses. These findings highlight the need for continued vaccine eval-uation, particularly in resource-limited settings, to inform public health strategies and optimize vaccination programs.