The Serum Institute of India on Thursday said that it will stop phase three trials of the Oxford coronavirus vaccine and review the situation till they begin again in the United Kingdom.

“We are reviewing the situation and pausing India trials till AstraZeneca restarts them,” the institute said in a statement on Thursday. “We are following DCGI’s instructions and will not be able to comment further on the same. You can connect with DCGI for more updates on this front.”

The Serum Institute of India is developing the vaccine in collaboration with AstraZeneca and Oxford University. On Wednesday, the Serum Institute of India said that its trials of the coronavirus vaccine will continue, even as United Kingdom-based pharmaceutical major AstraZeneca has suspended it. Following this, on the same day, the Drugs Controller General of India issued a notice to the Serum Institute of India, asking why the trials were not suspended till patient safety is established.

After the notice was issued on Wednesday, the institute tweeted: “We (Serum Institute of India), were going by DCGI’s direction and were not instructed to pause the trials. If DCGI has any safety concerns, we will adhere to their instructions and abide by the standard protocols.” The institute’s earlier decision to not pause the trials had attracted significant criticism from the medical fraternity.

The “Oxford vaccine” has been widely seen as one of the leading candidates against the infection. The vaccine, called AZD1222, had produced an immune response against the coronavirus and proved to be safe in early-stage clinical trials, according to results published in medical journal The Lancet.

In a statement on Tuesday, AstraZeneca said it was a “routine” pause because of “a potentially unexplained illness” of a volunteer. AstraZeneca said that in large trials, illnesses sometimes happen by chance, and added that it was working to expedite review of this to minimise any potential impact on the vaccine timeline.

According to The New York Times, the participant is from the United Kingdom and was found to have transverse myelitis, an inflammatory syndrome that affects the spinal cord and is often sparked by viral infections. The report said it remains unclear whether the illness was directly linked to AstraZeneca’s vaccine.

As many as 17 sites in India are conducting testing for the vaccine. It is being tested on individuals between the ages of 18 and 55. The trials began on August 26.

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Coronavirus: Drugs regulator sends notice to Serum Institute of India for not halting vaccine trials