Effectiveness of COVID-19 vaccines against SARS-CoV-2 infection among healthcare workers: a prospective cohort study

Introduction A vaccine's ability to protect against disease acquisition is considered one of its most important aspects of effectiveness. The study aimed to determine the effectiveness of COVID-19 vaccines among healthcare workers (HCWs). Materials and methods This was a prospective cohort study conducted with HCWs from April 2021 to May 2022. Vaccination data and PCR-confirmed infections were extracted from the Comprehensive COVID-19 Information System. Vaccine effectiveness for AZD1222 (ChAdOx1 nCoV-19), Sinopharm (BBIBP-CorV), and Sputnik V was evaluated using incidence rates per 100,000 person-days and multivariable time-dependent Cox regression models adjusted for age, sex, and occupational characteristics. Result Among the 3365 participants, all individuals received at least one dose, 95.3% received at least two doses, and 36.7% received a three doses of the COVID-19 vaccine. During follow-up, 517 SARS-CoV-2 infections were identified, with an overall incidence rate of 42.65 per 100,000 person-days (95% CI: 39.12–46.49). Vaccine effectiveness increased with successive doses.The overall effectiveness after three doses was estimated at 92% (95% CI: 81–97). By vaccine type, effectiveness after three doses was highest for AZD1222 (98%; 95% CI: 96–97), followed by Sinopharm (93%; 95% CI: 42–99) and Sputnik V (83%; 95% CI: 13–97). Higher infection rates were observed among females and certain occupational groups with greater exposure risk. Conclusion Completion of the COVID-19 vaccination schedule, including booster doses, markedly reduces SARS-CoV-2 infection risk among healthcare workers. Vaccine effectiveness increased with successive doses, peaking after the third dose. AZD1222 demonstrated the highest effectiveness, while all vaccines provided substantial protection.