Serum Institute may conduct more tests to get half-dose efficacy

In Brazil, two full doses of the vaccine were given one month apart, involving 8,895 participants and appeared to be 62 percent effective, while half dose, followed by a full dose, was given in the UK, involving a much smaller subset of 2,741 participants. Here the vaccine demonstrated 90 percent effectiveness. The average efficacy of both the dosing regimens put together was 70.4 percent.

According to the report, in India, Covishield is being administered as two full doses 28 days apart to over 1,600 participants. An official told the newspaper that SII, since it had sought permission to test the full dose regimen, can only seek permission to administer the vaccine in a full dose regimen.

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"... They (SII) have to ask for (emergency use authorisation) for full dose regimen only," an official told the newspaper, adding that if they ask marketing permission for half-dose, trials for that will have to be conducted.

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According to an official, the testing for this additional regimen may not be as drawn out, though, since SII could apply to the Central Drugs Standard Control Organisation (CDSCO) to include the testing as a "separate arm" in the ongoing vaccine trials in India.

"If they are using only the full-dose regimen, it is likely that Covishield may come out with a similar efficacy readout of around 60 percent. This would be still enough for them to apply for approvals from Indian drug regulator, because its guidelines suggest that a vaccine has to meet efficacy of around 30 to 50 percent for a COVID-19 vaccine to receive approval," vaccine expert Dr Davinder Gill told the newspaper, adding that while a lower efficacy might not be an issue at this point, it might make a difference a year from now.