A combination of Covishield and Covaxin doses produces a more potent immune response against SARS-CoV-2 and its variants than two jabs of the same vaccine, a preliminary study by the Indian Council of Medical Research has found.
The researchers studied 18 out of 20 individuals who were mistakenly given Covishield as the first jab and Covaxin as the second in Uttar Pradesh in April-May this year. The individuals’ blood samples were analysed at different stages for 60 to 70 days after vaccination.
“The mix-and-match of Covishield and Covaxin as first and second dose provoked a superior immune response than two doses of either vaccine,” said senior ICMR scientist Rajni Kant, the study’s lead investigator.
This is the first report of mixed immunisation using an adenovirus vector-based Covishield and an inactivated whole virion-based Covaxin in humans that has demonstrated safety and significantly improved immune response.
The findings are important as experts have asked if Covishield and Covaxin doses can be mixed to get around supply shortages. Currently, deliberate mixing of the two vaccines is not advised.
The findings could also have a significant bearing on the Covid-19 vaccination programme — a heterologous (mix-and-match) approach to immunisation could pave the way for strategies that provide better protection against variants.
But to conclusively prove these findings, the ICMR researchers said a multicentre randomized controlled trial would be needed. A vaccine’s immunogenicity is the ability of a foreign substance, such as vaccine-induced antigen (virus particles), to provoke an immune response.
Kant said, “The immunogenicity profile against Alpha, Beta, and Delta variants in the group that received Covishield and Covaxin was superior. The IgG antibody and neutralizing antibody response of the participants were also significantly higher compared to that in homologous groups, in which participants had received two doses of either Covishield or Covaxin.” Another investigator in the study, senior scientist Pragya Yadav of the ICMR-National Institute of Virology, said, “The findings suggest immunisation with a combination of an adenovirus vector platform-based vaccine (Covishield) followed by an inactivated whole virus vaccine (Covaxin) is not only safe but also elicits better immunogenicity.”
In other countries too, scientists are testing combinations of Covid-19 vaccines that have already been deployed. In May, researchers in Spain found that mixing shots had produced a vastly higher antibody responsem 14 days after receiving a Pfizer booster that followed an initial dose of the AstraZeneca jab (which is Covishield in India).