Covishield, Covaxin combination brings better immunogenicity than 2 doses of same vaccine: Study

Combining Covishield and Covaxin as first two doses of Covid-19 vaccines have shown "better immunogenicity" than the two doses of same vaccines, a study by the Indian Council of Medical Research (ICMR), which is yet to be peer reviewed, has said.

The ICMR study involved 98 people of which 18 had inadvertently received Covishield as first dose and Covaxin as the second dose in Uttar Pradesh. Out of the 18, seven were women.

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The study 'Serendipitous Covid-19 Vaccine-Mix in Uttar Pradesh, India: Safety and Immunogenicity Assessment of a Heterologous Regime' said 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.

"This study demonstrates that immunization 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," the study, which was uploaded on medRxiv, a preprint server.

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The researchers said such mixed regimens will also help to overcome the challenges of shortages 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, it added, to conclusively prove these findings a multicentre RCT needs to be carried out.

The researchers said this appeared to be the first such study on administering an adenovirus vectored vaccine followed by an inactivated whole virus vaccine.

The country has been following homologous prime-boost approach in Covid-19 vaccination but 18 people in Siddharth Nagar of Uttar Pradesh inadvertently received Covishield as the first jab and Covaxin as the second.

This incident happened in the fourth month of the national Covid-19 vaccination programme and it raised "considerable anxiety" among the public with a potential to contribute to vaccine hesitancy, the study, whose duration was from May to June this year, said.

"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 said.

"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.