95% seropositivity after two doses of Covishield, Covaxin in 515 healthcare workers: Study

A new pan India study found that among 515 healthcare workers, 95 per cent showed seropositivity after two doses of Covishield as well as Covaxin. Out of 425 Covishield and 90 Covaxin recipients, 98.1 per cent and 80 per cent, respectively, showed seropositivity, stated the study published in preprint server medRxiv on June 4.

Seropositivity means having the presence of antibodies in blood serum. Dr Awadesh Kumar, lead researcher of the study from GD Singh Hospital and Diabetes Institute, said the study found that both vaccines were equally good and could produce high antibodies even after a single shot.

The study was conducted across 13 states and 22 cities and found that the vaccines could generate an immune response in 95 per cent recipients, 21 to 36 days after the second dose. Seropositivity was observed in 98 per cent of those immunised with Covishield as opposed to 80 per cent in Covaxin recipients.

Authors, however, said the study was not a comment on which was the better vaccine. The study was to check on real-world effectiveness of the vaccine, they said.

“Our primary aim was to analyse antibody response (seropositivity rate and antibody titre) following each dose of both vaccines and its correlation to age, sex, blood group, body mass index and co-morbidities,” researchers said.

Anti-spike antibody titre is being measured at four time points: day 21 after the first dose until day before the second dose; day 21 to 28 of the second dose; day 83 to 97 (three months) and day 173 to 187 (six months) after the second dose. Second blood samples (5 ml) were collected from those eligible from day 21 to 36 after the second dose of each vaccine. A total of 515 (305 male, 210 female) participants took part in the study, of which 425 and 90 received both doses of Covishield and Covaxin, respectively.

The seropositivity rate was significantly higher in Covishield as opposed to Covaxin recipients (98.1 per cent v 80 per cent, respectively). Seropositivity rate was significantly more in participants aged above 60 (96.3 per cent) as opposed to 87.2 per cent in those aged below 60, in overall cohorts, primarily contributed by Covishield recipients, authors stated. Breakthrough infections were noted in 5.5 per cent (22/399) cohorts in Covishield and 2.2 per cent (2/93) of Covaxin recipients. Majority had mild (28/30) to moderate (2/30) Covid-19 infections and all recovered.

Dr Samiran Panda, head of epidemiology and communicable division at Indian Council of Medical Research, told The Indian Express that they were looking at a population level data, and taking samples from a certain group (like healthcare workers, for instance, in this study) may not indicate an extrapolation of inference in a wider group of people.