December 10, 2023


Indian Council of Medical Research (ICMR) in a study found that, mixed Covid immunisation routine, with a dose of Covishield followed by one of Covaxin, is safe and produces a better immune response as compared to the uniform two doses of any of the two vaccines.


  • Study titled ‘Serendipitous Covid-19 Vaccine-Mix in Uttar Pradesh, India: Safety and Immunogenicity Assessment of a Heterologous Regime’ was led by ICMR scientist Rajni Kant.
  • These findings had an important implication for Covid-19 vaccination programme wherein heterologous immunisation would open way for induction of improved and better protection against variant strains of SARS-CoV-2.
  • These mixed regimens of the vaccine will also help in overcoming the challenges of shortfall of particular vaccines and remove hesitancy associated with vaccines in people’s mind.
  • However, to prove these findings, a multicentre random clinical trial is needed to be carried out.
  • Study also found that, no major systemic adverse events were reported. Furthermore, reactogenicity profile of participants of heterologous group (mixed vaccine) was comparable to homologous groups.

How study was conducted?

ICMR Study followed 18 Uttar Pradesh residents who inadvertently received mixed doses, when vaccination plan was expanded. It also followed 40 recipients each of Covishield and Covaxin. However, the sample size of 18 participants was small. Therefore, a larger trial was needed to corroborate findings of the study.

WHO on mixed doses

Chief scientists of World Health Organization had recently advised individuals against mixing and matching COVID-19 vaccines from different manufacturers and said that, such decisions should be left to public health authorities. In June 2021, WHO’s Strategic Advisory Group of Experts on vaccines however noted that, Pfizer Inc vaccine could be used as second dose following the initial dose of AstraZeneca, if the latter is not available. But final words on mixed doses is yet to come from WHO.

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