COVID-19 Vaccine Effectiveness in Preventing SARS-CoV-2 Infection and Antibody Response Among Health Care Workers in Base Hospital Wathupitiwala, Sri Lanka

Background: Real-time data on COVID-19 vaccines among Healthcare Workers (HCWs) in low-income settings are crucial to the ongoing global vaccination programs. This study aimed to determine the Vaccine Effectiveness (VE) in reducing the risk of symptomatic COVID-19 infection, hospitalization, mortality and the dynamics of post-vaccination antibody titres in Sri Lankan health care workers Methodology: This longitudinal cohort study was conducted at Base Hospital Wathupitiwala from January 31st to October 31st, 2021. Blood samples were collected four weeks after the first COVISHIELD dose, one month after the first and second doses and seven months after the first dose. Healthcare workers were monitored for 8 months for symptomatic disease. Results: Antibody titres in vaccinated groups were significantly higher compared to the unvaccinated counterparts during the study period. The increase in antibody levels after the second dose of COVISHIELD/ChAdOx1 nCoV-19 vaccination, compared to the first dose, was notably high, while a significant decline in antibody levels was observed after a 7-month period. Only mild to moderate vaccine-induced adverse reactions were reported following the first dose of COVISHIELD/ChAdOx1 nCoV-19, with no adverse reactions other than site-specific local reactions reported for the subsequent dose. Overall, the adjusted vaccine effectiveness of COVISHIELD against symptomatic infection was 68% (95% CI: 25%, 87%) and for Sinopharm, it was 58% (95% CI: -4%, 80%). The adjusted vaccine effectiveness with two doses of COVISHIELD was higher among males, younger age groups and individuals with a BMI lower than 25. Conclusion: The results have important clinical implications, supporting the rationale for full vaccination with both doses, possibly with boosters, especially for high-risk populations like healthcare workers.