Post-Vaccination Symptomatic SARS-CoV-2 Infections are Minimal and Non-Serious: An Observational Multicenter Indian Cohort Study of 28342 Healthcare Workers

Abstract

Background: The healthcare workers (HCWs) have been on the frontline in combating the pandemic and were prioritized for vaccination when COVID-19 vaccines became available. Although vaccines effectively prevent infection in most cases, some cases of post-vaccination infections have been reported, raising concerns about vaccine efficacy. This study investigated the efficacy of COVID-19 vaccines in preventing and reducing the severity of post-vaccination infections (PVI) among HCWs. Methods: This observational study examined 28342 vaccinated HCWs with SARS-CoV-2 (symptomatic severe acute respiratory syndrome coronavirus 2) infections during the initial five months of vaccination (January 16-June 15, 2021). They worked at 43 Apollo Group hospitals in 24 Indian cities. PVI was investigated after recombinant ChAdOx nCOV-19 (Recombinant) or the whole virion inactivated Vero cell vaccines were administered. Various parameters were evaluated such as age, sex, time to infection, type of vaccine, infections after a single and two doses, monthly and regional case distribution, clinical severity of infection, hospitalization and intensive care unit (ICU) requirement, and death. Findings: Symptomatic PVIs occurred in a low percentage of vaccinated cohorts (5⸱07%, p<0⸱001), and these were predominantly mild and did not result in hospitalization, ICU admissions (p<0⸱0001), or death. Both vaccines provided similar protection, with PVI incidences of 5⸱11% and 4⸱58%, following ChAdOx nCOV-19 (Recombinant) and the whole virion inactivated Vero cell vaccines, respectively (p50 years significantly contracted more infections(p<0⸱001 and p=0⸱001, respectively). Two-dose vaccination has significantly lower odds of developing PVI (0.83, 95%CI – 0.72 to 0.97). Maximum infections occurred during the peak of the second COVID-19 wave from mid-April to May 2021 (p<0⸱001). No significant difference existed in the infection between sex, vaccine type, and the number of vaccine doses received (p≥0⸱05). Interpretation: PVI occurred in a small percentage of HCWs. Vaccination protected them significantly from the infection but also severe disease. Funding Information: None. Declaration of Interests: None. Ethics Approval Statement: This study was approved by an Ethical Institutional Committee (EIC), and a consent waiver was given by the EIC.