A GROUP of 18 people, who had "inadvertently received Covishield as the first jab and Covaxin as the second", showed better immunogenicity — the ability to generate an immune response — than those who received two doses of the same vaccine, according to a new study by the Indian Council of Medical Research (ICMR), reports The Indian Express.
In May, 18 villagers in Siddarthnagar, Uttar Pradesh, had received Covaxin as the second dose, six weeks after they got Covishield. The study compared their reaction to 40 recipients of two doses of Covishield and 40 recipients of two doses of Covaxin.
"We compared the safety and immunogenicity profile of them (the group of 18) against that of individuals receiving either Covishield or Covaxin. Lower and similar adverse events following immunisation in all three groups underlined the safety of the combination vaccine-regime," said the study which is yet to be peer reviewed.
"Immunogenicity profile against Alpha, Beta and Delta variants in the heterologous group was superior; IgG antibody and neutralising antibody response of the participants was also significantly higher compared to that in the homologous groups," it said.
"Overall, this study demonstrates that immunisation with a heterologous combination of an adenovirus vector platform-based vaccine followed by an inactivated whole virus vaccine is safe and elicits better immunogenicity than two doses of homologous vaccination, using the same vaccines," it said.
While Covishield is built on a viral vector vaccine platform and uses a weakened version of adenovirus, a common cold virus that causes infection in chimpanzees, Covaxin is built on an inactivated whole virus vaccine platform.
The study is the first scientific evidence emerging from India on superior immunogenicity profile demonstrated in mixed-vaccine doses. However, the researchers have underlined that to conclusively prove these preliminary findings, "multi-centre" randomised control trials need to be carried out. They have also flagged the study's limitations: the sample size of 18 participants is small; follow-up period is only 60-70 days after first dose; baseline serological and immunological data of participants is not available.
According to the study, the findings have an "important implication" for the Covid-19 vaccination programme wherein "heterologous immunisation will pave the way for induction of improved and better protection against the variant strains of SARS-CoV-2".
"This is the first report of heterologous immunisation with an adenovirus vector based and an inactivated whole virion vaccine in humans demonstrating safety and significantly improved immunogenicity… Immunogenicity profile studied against the variants of concerns, Alpha, Beta and Delta variants, demonstrates significantly higher titers in the heterologous group," it said.
The researchers have said such mixed regimens will help to "overcome the challenges of shortfall of particular vaccines" and "remove hesitancy around vaccines in people's mind that could have genesis in programmatic 'errors' especially in settings where multiple Covid-19 vaccines are being used".
On safety, reactogenicity analysis showed that in the heterologous group, 11 per cent reported pain at the injection site; however, during the second dose, no such local adverse event was reported, it said.
The most commonly reported systemic adverse event was pyrexia (raised body temperature) and malaise (discomfort): 33.3 per cent reported this during the first dose, and 5.5 percent during the second dose. "No other systemic AEFI like, urticaria, nausea, vomiting, arthralgia or cough was reported," said the study.
Currently, the Indian drug regulator has granted permission to CMC Vellore to conduct Phase 4 clinical trials to assess the efficacy of a combination of Covishield and Covaxin doses as compared to the current protocol of using two doses of the same vaccine