Two doses of Covishield vaccine produced more antibodies than Covaxin doses, but there were relatively fewer instances of ‘breakthrough infections’ after the latter, reports a study of healthcare workers in India.
The study is being peer-reviewed and has been submitted to a journal but appears as a preprint in MedrXiv, an online repository, and is among the few studies of the real world effectiveness of vaccination in India. The study, by a collective of doctors, shows that none of the participants, who were also all doctors and got both doses of vaccines, were ill and only about 6% tested positive at different points of the vaccination schedule. While both vaccines were protective, there were differences in the protection accorded by a single dose of the vaccines. 515 healthcare workers from 13 States and covering 22 cities were evaluated from January to May 2021. Their blood samples were also tested for the presence, quantity of antibodies produced and levels of the specific antibodies that are directed to the spike protein of the virus, widely held to be a proxy of protection. A single dose of Covishield elicited about 10 times the antibodies than Covaxin whereas a second dose narrowed the gap somewhat, with Covishield-triggered antibodies about six times that of Covaxin-stimulated ones, the study found. Though the spike protein remains the key target of most vaccines, ICMR and Bharat Biotech, the makers of Covaxin, have previously said that being a vaccine made out of an inactivated virus, it elicited a ‘broader immune’ response, meaning antibodies aimed at different parts of the coronavirus to neutralise it. T cell immunity, that is reported to elicit a longer lasting protection wasn’t measured in the study. While real world efficacy data of Covaxin and India-centric data on Covishield isn’t public yet, recent studies have shown that most vaccines including Covaxin and Covishield have reduced response to some coronavirus variants such as them .
The study authors also evaluated the relationship of immune response to gender, a history of testing positive for COVID prior to vaccination and co-morbidities. Dr A.K. Singh, of the GD Hospital and Diabetes Institute, Kolkata and among the authors of the paper, said the greater number of infections after the second wave was probably due to the increased number of cases after April and the high exposure of the study participants all doctors in COVID hospitals to patients during the second wave.
By G Gnana Priya dharshini