Objective: Real-world studies assessing the effectiveness of the BBIBP-CorV vaccine in low and middle-income countries are limited. We evaluated the BBIBP-CorV vaccine's effectiveness in reducing COVID-19 symptomatic disease, hospitalisation, severe disease, and mortality during the third wave of the pandemic in Sri Lanka. Methods: We conducted a test-negative case-control study in North Central Province from May 2021 to February 2022. Evidence of vaccination was obtained from the national registry. The PCR-positive patients were cases, while negative individuals were controls. Adjusted vaccine effectiveness (aVE) was computed for fully, partially, and non-vaccinated groups in reducing symptomatic disease, hospitalisation, severe disease, and mortality. Results: Our study involved 3305 cases and 3418 controls. The overall aVE for preventing PCR-positive infection in fully vaccinated was 30·8 % (95 % CI:17·9–41·6). In fully vaccinated over 60 years, the overall aVE was 72·3 % (95 % CI: 49·7–84·8). Full vaccination with BBIBP-CorV is effective in reducing hospitalisation, severe COVID-19 disease, and death, with aVE rates of 70·3 % (95 % CI: 57·9–79·0), 88·9 % (95 % CI: 81·8–93·2), and 92·3 % (95 % CI: 84·8–96·1) respectively. Conclusion: Individuals who have received two doses of the BBIBP-CorV vaccine are protected against hospitalisation, severe COVID-19 disease, and death. Duration of protection against hospitalisation, severe COVID-19, and fatal COVID-19 sustained at least 121 days, with no sign of waning during that time.
