A combination of Covishield and Covaxin vaccines elicits better immunogenicity than two doses of the same vaccine, the Indian Council of Medical Research (ICMR) said on Sunday.
The Council released its findings which 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.
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.
The pre-print report titled “Serendipitous COVID-19 Vaccine-Mix in Uttar Pradesh, India: Safety and Immunogenicity Assessment of a Heterologous Regime,” has not been certified by peer review and should not be used to guide clinical practice, the Council said.
It, however, maintained that the findings have an important implication for the COVID-19 vaccination program wherein heterologous immunisation will 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 have genesis in programmatic ‘errors’ especially in settings where multiple COVID-19 vaccines are being used. However, to conclusively prove these findings a multicentre RCT needs to be carried out,” the ICMR said.
Previously the World Health Organisation had warned against mixing of vaccines, saying there was very little information on the mix-and-match of vaccines. It advised against people mixing and matching vaccines from different manufacturers, calling it a “dangerous trend” since there was little data available about the health impact.
The Council admitted that there are few limitations to their study. “The sample size was small and the participants were put under a short follow up period of only 60-70 days after immunisation with the first dose and baseline serological and immunological data of the participants not available,” it said.
It, however, added that there are several major strengths in the study. “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,” it noted. Additionally comparable proportion of solicited adverse event following immunization in the heterologous and homologous groups despite the elderly age group (mean age 62 years) demonstrates the safety of combination regimen.