On the basis of a trial research, the Indian Council of Medical Research (ICMR) bats for the mixed doses of COVID-19 vaccination. It said that 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 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.

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.

The WHO is yet to issue guidance on mixing of vaccine doses. 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.

“Despite the high median age of the participants of the heterologous group (62 years) which got mixed vaccine in our study, the reactogenicity profile demonstrated that mixing of the two vaccines based on different platforms is safe,” the study shows.

The study followed 18 Uttar Pradesh residents who inadvertently received mixed doses when the inoculation plan was expanded and 40 recipients each of COVISHIELD and COVAXIN. The study authors say the sample size of 18 participants was small and, therefore, a larger trial was needed to further corroborate the findings of the current study. The authors said theirs was the first report of heterologous (mixed vaccines) immunisation with an adenovirus vector-based and an inactivated whole virion vaccine in humans demonstrating safety and significantly improved immunogenicity.

COVISHIELD (Oxford-Astrazeneca) and COVAXIN are the two leading indigenous vaccines being used to inoculate the country's vulnerable population. While both the vaccines have been proven to be quite efficacious and safe for use in their own ways, expert committees are now contemplating mixing doses of both the traditional vaccines to ramp up benefits and offer longer-term immunity.

Now, while mixing and matching coronavirus vaccine shots isn't entirely new, it's the first time, two vaccines of a similar kind are being proposed to be mixed together.

The proposed plan to mix doses of COVISHIELD, manufactured by Pune-based Serum Institute of India (SII) and Hyderabad-based Bharat Biotech's COVAXIN has been suggested by The Subject Expert Committee (SEC) on vaccine usage.

The two vaccines, while both made using traditional vaccine-making technologies are slightly different in comparison. The Astrazeneca vaccine is an adenovirus vector and contains a weakened (harmless) version of the common cold virus, which has been further genetically modified to match the coronavirus (but cannot cause the illness). Meanwhile, COVAXIN, makes use of an inactive strain, aka, a dead virus to instruct the immune cells to prompt an antibody response in the future run.

Preliminary studies and real-world observations have showcased that while COVAXIN boasts of an efficacy rate that could vary between 70-81%, COVISHIELD, which has also been shown to considerably cut down rates of hospitalization and mortality with the disease, has an efficacy rate of 78%. The efficacy rates, however, do tend to come down with the Delta variant, but nonetheless, the vaccines are workable on many fronts.

Mixing and matching of Covaxina and Covishield isn't the first time such a policy has been considered. Ever since mutant strains of the virus have come into circulation, and waning immunity with some of the vaccines becoming a cause of concern, the mix and match regimes have been subject to a number of clinical studies. However, there's no relevant, or substantial data to support the safety as yet.

While the variant continues to spread in a rampant manner across the world, and similarly harmful variants speculated to prop up, it is believed that mixing vaccines will allow greater immunity that works against the variant and prompts a longer-lasting antibody count which could protect individuals. With variants, experts also believe that mixing vaccines based on two different technologies could also prompt the immune system to develop a wider response.