A study by Indian Council of Medical Research involving 98 people, 18 of whom had inadvertently received Covishield as first dose and Covaxin as the second in Uttar Pradesh, showed that combining these two COVID-19 vaccines elicited better immunogenicity than two doses of the same vaccine.
The study, which is yet to be peer reciewed, also found that immunisation with combination of Covishield and Covaxin was safe and the adverse effects were found to be similar when compared to the same dose regimen.
"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 study was conducted against the backdrop of the event of mixed dosing raising considerable anxiety in public domain, with a potential to contributing to vaccine hesitancy.
The 18 individuals, who had inadvertently received Covishield as first dose and Covaxin as the second along with, 40 recipients of two doses of Covishield and 40 recipients of two doses of Covaxin, were recruited for the study, which took place from May to June 2021.
"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,” read the study.
Stating that the "Immunogenicity profile against Alpha, Beta and Delta variants” was superior in case of those receiving mixed vaccine doses, the study said that, “IgG antibody and neutralising antibody response of the participants was also significantly higher compared to that in the homologous groups."
"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.
With regards to any adverse effects following immunisation (AEFI), none of the participants enrolled in the study had any serious AEFI within 30 minutes of immunisation with the first or second dose.The reactogenicity analysis was carried out based on solicited local and systemic AEFIs reported in the three groups within seven days of immunisation.
Besides the most common local AEFI, pain at injection site, reported after first and second dose, no other AEFI was reported.
According to the study, the most commonly reported systemic AEFIs were fever, of low to moderate grade, which subsided in all participants within three to four days, and malaise
"Despite the high median age of the participants of the heterologous group (62 years) in our study, the reactogenicity profile demonstrated that mixing of the two vaccines based on different platforms is safe," the study said.
Highlighting the implication of these findings for the COVID-19 vaccination program, including improved and better protection against the variant strains of SARS-CoV-2, the study said, “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 randomised clinical trial needs to be carried out, the study underlined.
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.
The immunisation program against COVID-19 in India started with two vaccines—the adenovirus vector platform-based vaccine Covishield and inactivated whole virion BBV152 Covaxin—and homologous prime-boost approach (i.e. the antigen was delivered using the same vectors) was followed.
However, in the fourth month of the nationwide vaccination program 18 individuals, at a primary health centre, in Siddarthnagar, Uttar Pradesh inadvertently received Covishield as the first jab and Covaxin as the second.