The Indian Council of Medical Research (ICMR) said a mixed Covid immunisation routine, with a dose of Covishield followed by one of Covaxin, was safe and elicited a better immune response than the regime where uniform two doses of any of the two vaccines were administered.
The study was only conducted on 18 people of Uttar Pradesh’s Siddharth Nagar, who by mistake received two doses of two separate vaccines. The study, titled ‘Serendipitous Covid-19 Vaccine-Mix in Uttar Pradesh, India: Safety and Immunogenicity Assessment of a Heterologous Regime’, also found that no major systemic adverse events were reported and reactogenicity profile of the participants of heterologous group (mixed vaccine) was comparable to homologous groups.
The immunisation programme against COVID-19 in India started with two vaccines — AstraZeneca’s ChAdOx1-nCov-19 (named Covishield in India) and inactivated whole virion BBV152 (Covaxin). A homologous prime-boost approach was followed.
However, 18 individuals, under the national program, inadvertently received Covishield as the first jab and Covaxin as the second. In its study, the ICMR has compared the safety and immunogenicity profile of these persons against that of individuals receiving either Covishield or Covaxin.
Led by ICMR scientist Rajni Kant, the study said the findings had an important implication for the Covid-19 vaccination programme wherein heterologous immunisation would pave the way for induction of improved and better protection against the variant strains of SARS-CoV-2.
“Such mixed regimens will also help to overcome the challenges of shortfall of particular vaccines and remove hesitancy around vaccines in people’s mind that could Mixed Covishield, Covaxin doses. However, to conclusively prove these findings, a multicentre random clinical trial needs to be carried out,” say study authors at a time when the WHO is yet to issue guidance on mixing of vaccine doses.
An earlier study had found similar findings in a mouse model: “The immunisation with a heterologous combination of an adenovirus vector platform-based vaccine (Covishield) followed by an inactivated whole virus vaccine (Covaxin) is safe and elicits better immunogenicity than two doses of homologous vaccination using the same vaccines,” said the study, published as a pre-print but yet to be peer-reviewed.
