Pharma major AstraZeneca has “paused” the late-stage clinical trials on the AZ-Oxford University Covid-19 vaccine candidate due to a “potentially unexplained illness” in one participant in the UK.

“As part of the ongoing randomised, controlled global trials of the Oxford coronavirus vaccine, our standard review process was triggered and we voluntarily paused vaccination to allow review of safety data by an independent committee,” an AZ note said.

The AZ-Oxford University candidate is among a handful of Covid-19 vaccines that are in large-scale advanced trials across the world, the final leg before regulatory approvals are received for mass use.

Serum Institute of India has a production and supply alliance on this vaccine in low-and-middle income countries. The vaccine-maker, however, said India trials on the AZ-Oxford vaccine candidate were not impacted.

But the Drugs Controller General of India issued a show-cause notice to Serum Institute for not informing it about AstraZeneca pausing the clinical trials of the Oxford vaccine, a PTI report said. “Serum Institute... till now has not informed the Central licensing authority regarding pausing the clinical trial carried out by AstraZeneca in other countries and also not submitted casualty analysis of the reported serious adverse event with the investigational vaccine for the continuation of phase 2 and 3 clinical trials of the subject vaccine in the country in light of the safety concerns,” read the show-cause notice.

A person familiar with the trial said the Indian regulator had called for a 7-day gap after the first shot of the two-dose vaccine was given, for a safety review. This happened last week, and details are expected from AZ before the safety review is completed and the trial continues, the official said.

To query from BusinessLine , earlier in the day, on the pausing of trials, Serum Institute had said: “We can’t comment on the UK trials, but they have been paused for review and they hope to restart soon. As far as Indian trials are concerned, they are continuing and we have faced no issues at all.”

Earlier on Wednesday, AZ said the “routine action” (pausing the trial) was taken to maintain the integrity of the trial, while the adverse event was being investigated. In large trials, illnesses will happen by chance but must be independently reviewed... We are working to expedite the review to minimise any potential impact on the trial timeline,” the company said.

Clarity is awaited from AZ and the Oxford University on the adverse event. Besides the UK, the US, Brazil, South Africa and India are participating in Phase II/III trials.

According to interim results published in July, the candidate AZD1222 “was tolerated and generated robust immune responses against the SARS-CoV-2 virus in all evaluated participants,” an AZ note had said.

Not unexpected

Arun Bhatt, a regulatory expert on clinical research, said the adverse event, “though not unexpected, was serious”. Foreign media reports indicate it was “transverse myelitis”, an inflammation of the spinal cord that can lead to paralysis, bladder, bowel dysfunction, he said.