The regime for both the vaccines initially included a second homologous booster dose following a priming dose at an interval of 4 weeks. With gradually emerging evidence, the gap between the two doses of Covishield was increased to 6-8 weeks and later to 12 weeks.
"The findings suggest that immunisation with a combination of an adenovirus vector platform-based vaccine followed by an inactivated whole virus vaccine was not only safe but also elicited better immunogenicity," revealed the study led by Pune-based National Institute of Virology (NIV). The study is not yet peer-reviewed and has been published pre-print on medRxiv.
During the national vaccination programme, 18 people from Audai Kalan village of Siddharthnagar district of eastern Uttar Pradesh, after receiving Covishield as the first dose, were inadvertently administered Covaxin in the second dose after an interval of six weeks.
The study compared the safety and immunogenicity profile of them against that of individuals receiving either Covishield or Covaxin in both doses.
The results showed that the people in the mix and match group had superior immunogenicity profiles against Alpha, Beta and Delta variants of Covid-19. The IgG antibody and neutralising antibody response of the participants was also significantly higher compared to other groups, the ICMR said.
The study reported no major adverse events.
"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," the ICMR said
"Such mixed regimens will also help to overcome the challenges of the 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," added the apex medical body.