Serosurveillance among healthcare workers vaccinated with ChAdOx1 nCoV-19 Corona vaccine in a tertiary hospital of Kerala, India: prospective cohort studу

Aim. To evaluate antibody responses following two doses of ChAdOx1 nCoV-19 Corona vaccination in a tertiary care setting and the association of host factors like age, body mass index and comorbidities in determining this antibody response.

Materials and methods. This prospective serosurveillance study was done among healthcare workers of Jubilee Mission Medical College, vaccinated during January- April 2021. Blood samples were drawn from 170 participants after their first dose and from 156 participants after their second dose of CovishieldTM to measure the specific Ig G antibodies against the recombinant S1 subunit of the S protein of SARS-CoV-2.

Results. The median level of anti-SARS-CoV-2 Ig G antibody 28–56 days after the first dose vaccination was 3.64 S/C (1.33, 7.24) and 11.6 S/C (8.61, 14.27) after 14 days of second dose vaccination. Protective levels of anti-SARS CoV-2 Ig G antibodies (≥ 9.5 S/C) was developed by 25 participants (14.7%, 95% confidence interval: 9.8% to 20.9%) after 28–56 days of first dose of vaccination and by 109 participants (69.9%, 95% confidence interval: 62% to 77%) after 14 days of second dose. Health care workers in the age group below 60 years (p = 0.027) and without comorbidities (p = 0.079) showed higher protective Ig G levels. But on multiple logistic regression only age under 60 years was found to be statistically significant.

Conclusion. After the first dose of the ChAdOx1 nCoV-19 vaccine, the formation of Ig G antibodies was observed, the level of which increased after the second dose. Among the various associated factors studied only the age of the participants below 60 years was found to be statistically significant for protective antibody levels. Follow up studies involving larger and different ethnic population is key to decoding the antibody response especially in the elderly and high-risk groups.