Six Months Follow-Up Study on Health Care Workers on Persistence of Antibodies to SARS-CoV-2 after Covishield Vaccination

BACKGROUND Efficacy of COVID vaccines has been evaluated in various studies. The interim analysis from four randomized controlled trials in UK, Brazil, and south Africa regarding efficacy of two doses of the vaccine was found to be 70.4% (95·8% CI 54·8–80·6). There is a limited data on follow-up Ab titer post vaccination. Hence, the current study is first of its kind with the objective to determine vaccine long term efficacy and its determinants. METHODS Health Care Workers (HCW) from Apollo Multispeciality Hospitals, Kolkata who underwent Covishield vaccination from January 2021 to April 2021 were included in the study. Serological testing was done prior to first and second dose of vaccinations, and additionally around six months post second dose. RESULTS Between January 2021 to April 2021, 2032 HCW, with predominant age of less than 30 years (44.83%) and male gender (61.96%) undergoing Covishield vaccination were enrolled. Antibodies were detected in 953 (46.9%) individuals prior to first dose, 1449 out of 1495 (96.9%) remained positive prior to second dose and 465 out of 504 (92.3%) HCW after 6 months and remaining 39 (7.7%) either had lost or never had antibodies in their blood. The mean ± SD value of first, second and third antibodies were 2.35 ± 3.10, 10.46 ± 4.84 and 8.75 ± 4.88 respectively. CONCLUSIONS This study provides long observation period, covering the complete progress of the pandemic which provides a “real-life” picture of the antibody level dynamics over time, and after vaccination.