India on Thursday extended the gap between the first and second doses of the Serum Institute-produced Oxford-AstraZeneca vaccine Covishield to 12-16 weeks from the existing six-eight weeks, amid a huge surge in corona cases and an acute shortage of jabs.

Covishield is also being used in Bangladesh's mega inoculation drives. Though Bangladesh has inked a deal with the Serum Institute to acquire 30 million doses of Covishield, a recent surge in Covid cases in India has made the delivery of the remaining doses uncertain.

"Based on available real-life evidence, particularly from the United Kingdom, the Covid-19 Working Group has agreed to increase the dosing interval between two doses of Covishield to 12-16 weeks," the Indian government said in a statement.

Prime Minister Narendra Modi rolled out the world's largest Covid vaccination drive in India on January 16. Covishield and local pharmaceutical company Bharat Biotech's Covaxin are currently being given to the citizens of India. 

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The Indian government has, however, not announced any changes in dosage intervals for Covaxin, which remains at four to six weeks. "No change in intervals for Covaxin was recommended," the statement said.

Serum's CEO Adar Poonawalla has welcomed the government's announcement. "This is beneficial both from efficacy and immunogenicity standpoints... good scientific decision to increase the gap," he told a local news channel.

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Poonawalla also cited a study in international medical journal The Lancet, linking widening of Covishield doses to increased efficacy.

India's main opposition Congress party has, however, expressed apprehensions over the government's latest move, given the fact that there has been a change in Covishield dosage intervals for the second time in three months.

"First, it was four weeks for the second dose, then six-eight weeks and now we are told 12-16 weeks. Is this because there are not enough stocks of vaccines or because professional scientific advice says so?" senior Congress leader Jairam Ramesh tweeted:

"Can we expect some transparency from the Modi government?" he added.

India is not only reeling under the twin burdens of a huge surge in Covid-19 cases and an acute shortage of jabs, but also facing a deadly crunch of medical oxygen. In the past one month, at least 120 patients have died at different hospitals in India due to oxygen shortage.

With Prime Minister Modi's government failing miserably to stem the oxygen crisis, the Supreme Court last week set up a 12-member National Task Force to assess the availability of the life-saving gas across the country and help resolve the crisis at the earliest.

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"The rationale for constituting a Task Force at a national level is to facilitate public health response to the pandemic based on scientific and specialised domain knowledge. We expect leading experts in the country shall associate with the Task Force," judges had said.