''I am against the mixing of two different vaccines. There is no need to mix two different vaccines,'' he said, when asked about a recent ICMR study that a cocktail of Covishield and Covaxin could generate better immunity. 

''If cocktail vaccines are administered and if the result is not good, then SII may say that another vaccine was not good, vice versa, the other company might say that since you mixed Serum's vaccine, it did not give desired results,'' Poonawalla said. 

The efficacy of this approach has not been proven in field trials involving thousands of participants, he added. A study by the 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 vaccines elicited better immunogenicity.

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