Antibody titres in fully vaccinated healthcare workers with and without breakthrough infection during the Delta and Omicron waves

INTRODUCTION: Assessment of antibody response to vaccination against SARS CoV2 has clinical, public health, and policy implications during the pandemic and in the context of future waves. METHOD: In this repeated cross-sectional study, we estimated total binding antibody levels to the spike protein of the SARS CoV2 virus post two doses of Covishield vaccine among 133 health care workers (HCWs) (phase 1), followed by antibody levels among a subset (n = 61) of this group at 9 months after the second dose (phase 2). The time period of the first and second blood collection corresponds to Delta and Omicron waves, respectively. RESULTS: We report 100% seroconversion post 28 days of the second dose of the Covishield vaccine among infection naïve HCWs. In this study, 33% had a breakthrough infection in phase 1 and 24% reported a history of infection in phase 2. The antibody titres were higher in the breakthrough infection group compared to the infection naïve group during both Delta and Omicron waves. CONCLUSION: This shows that there is a good seroconversion with two doses of vaccine, weaning of antibody with time, and a rise of antibody titre if infected with SARS CoV 2 subsequently.