Immunogenicity of ChAdOx1 (Covishield) Booster Dose in Healthcare Providers: A Pre-Post Study

Background Worldwide, healthcare workers who face a higher risk of contracting coronavirus disease 2019 (COVID-19) were among the first to receive COVID-19 vaccinations. Following the initial two vaccine doses, health experts recommended a third booster shot to enhance protection against the severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) virus. However, limited information about how this booster dose affects antibody levels is available. This study assesses the immune response triggered by the ChAdOx1 (Covishield) booster dose. Methods We conducted a before and after study among 132 healthcare providers at a tertiary care hospital in India who had already received their initial COVID-19 vaccine doses and agreed to participate. A booster shot was administered nine months following their second vaccine dose per the prevalent norms. We collected blood samples to measure immunoglobulin-G (IgG) levels against the spike protein's receptor-binding domain of the SARS-CoV-2 virus. These blood samples were taken both when they received the booster shot and one month after the booster. We determined IgG levels using a chemiluminescence microparticle immunoassay. Result Among the participants, approximately 54% were females. Regarding occupation, about 36% were doctors, 30% were students, 20% were nursing officers, and the remaining 14% held grade-4 positions. The median age of the participants was 32 years. About 74% had no history of underlying health conditions. Before the booster dose, 29% of the participants tested negative for antibodies. However, all participants developed antibodies following the booster shot, and there was a significant increase in antibody levels, which was statistically meaningful with a p-value of less than 0.0001. Conclusion In conclusion, the administration of a booster dose effectively induced seroconversion and significantly increased antibody levels among healthcare providers, enhancing their immunity against COVID-19, essential in the face of a waning immune response to primary series vaccination.