AbstractThe Oxford-Astra Zeneca COVID 19 vaccine (AZD1222 or ChAdOx1) is locally manufactured as Covishield by Serum Institute, Pune, India. In a group of 307 healthcare workers administered Covishield, we report measured antibody response to SARS-CoV-2 directed against the spike protein (S-antigen) at days 0, 7, 14, 28 and 45, with second dose on day 28 for all except 20 subjects who did not receive a second dose. In 129 subjects (42%) who had already developed antibodies to SARS-CoV-2 at day 0 (before immunization), it was observed that antibody response was significantly higher at each time point, with the maximum increase seen between days 0 and 7. The antibody levels and neutralizing activity in these subjects had peaked by day 28 and the second dose did not lead to further increase. Data from 9 subjects who were seropositive at baseline and received only one dose was similar to those who received both doses. In contrast the baseline sero-negative group (n=178) started developing antibody response only after 14 days or later. Administration of the second dose was associated with further increase in antibody levels at day 45 compared to day 28, with marked increase in neutralizing activity. In baseline seronegative subjects, who did not take the vaccine at day 28 (n=11), the antibody levels increased by about 2.5 folds between days 28 and 45, with minimal change in the neutralizing antibodies. In general, vaccination was well tolerated, and there were no group specific differences in post-vaccination symptomatology. Our data suggests that ChAdOx1 is highly immunogenic, particularly so where previous SARS CoV2 antibody-response is established. In such subjects, a single dose may be sufficient but in absence of such determination, both doses are required.
IgG anti-spike antibody levels in healthcare workers with and without prior COVID-19 up to 3 months after BNT162b2 vaccination