The study also found that immunisation with combination of Covishield and Covaxin was safe and the adverse effects were also found to be similar when compared to the same dose regimen.The study titled ‘Serendipitous COVID-19 Vaccine-Mix in Uttar Pradesh, India: Safety and Immunogenicity Assessment of a Heterologous Regime’ has been uploaded on medRxiv, a preprint server and is yet to be peer reviewed. 

“To the best of our knowledge, this is the first study which reports the effects of heterologous prime-boost vaccination with an adenovirus vectored vaccine followed by an inactivated whole virus vaccine,” the researchers said. The immunisation programme against COVID-19 in India started with two vaccines--adenovirus vector platform-based vaccine Covishield and inactivated whole virion BBV152 -Covaxin--and homologous prime-boost approach was followed. However, 18 individuals, under the national program, in Siddarthnagar, Uttar Pradesh inadvertently received Covishield as the first jab and Covaxin as the second. 

“We compared the safety and immunogenicity profile of them (18 individuals) against that of those receiving either Covishield or Covaxin. Lower and similar adverse events following immunisation in all three groups underlined the safety of the combination vaccine-regime. 

“Immunogenicity profile against Alpha, Beta and Delta variants in the heterologous group was superior and IgG antibody and neutralising antibody response of the participants was also significantly higher compared to that in the homologous groups,” the study stated. 

“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,” it said.