Mixed doses of Covishield and Covaxin provide better results: ICMR study

Combining the two COVID-19 vaccines, Covishield and Covaxin, elicits better immunogenity than two doses of the same vaccine, shows a study by Indian Council of Medical Research (ICMR).

The study involving 98 people, 18 of whom had inadvertently received Covishield as first dose and Covaxin as the second in Uttar Pradesh, also found that immunization with combination of both the vaccines was safe and the adverse effects were also found to be similar when compared to the same dose regimen.

The study, ‘Serendipitous COVID-19 Vaccine-Mix in Uttar Pradesh, India: Safety and Immunogenicity Assessment of a Heterologous Regime’, has been uploaded on medRxiv, an online server and is yet to be reviewed by experts.

“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.

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The immunization program 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.

The nationwide vaccination programme has entered its fourth month and the incident of mixed dosing raised considerable anxiety in public domain, and increases the vaccine hesitancy among public. The study was conducted against this backdrop. So, including these 18 individuals who had received one dose of Covishield and second dose of Covaxin, 40 recipients of two doses of Covishield and 40 recipients of two doses of Covaxin, were recruited in the study. The study was conducted for a duration of one month 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 immunization 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.

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“The findings suggest that immunization 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 added.

The reactogenicity analysis was carried out based on solicited local and systemic adverse events following immunization (AEFIs) reported in the three groups within seven days of immunization.

None of the participants enrolled in the study had any serious AEFI within 30 minutes of immunization with the first or second dose. The most common local AEFI reported after first and second dose was pain at injection site. No other local AEFI such as erythema, induration, pruritis or pustule formation was recorded by any of the participants. Most commonly reported systemic AEFI were pyrexia and malaise. No other systemic AEFIs like urticaria, nausea, vomiting, arthralgia or cough was reported. The pyrexia was of low to moderate grade and was managed by administration of paracetamol and subsided in all participants within three to four days post vaccination, according to the study.

“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.

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These findings have an important implication for the COVID-19 vaccination program, wherein heterologous immunization will pave the way for induction of improved and better protection against the variant strains of COVID-19.

“Such mixed regimens will also help to overcome the challenges of shortfall of particular vaccines and remove hesitancy around vaccines in peoples mind that could have genesis in programmatic errors, especially in settings where multiple COVID-19 vaccines are being used,” the study highlighted. However, according to the study, a multicenter RCT needs to be carried out to conclusively prove the findings of the study.