The announcement Tuesday by AstraZeneca that it had temporarily stopped Covid-19 vaccine trials due to illness to one or more participants could slow the availability of a safe vaccine to South American countries. Several countries in the region were part of AstraZeneca’s stage three trials.
The vaccine, developed in conjunction with Oxford University, has been described by the World Health Organization as probably the world’s leading candidate and the most advanced in terms of development. The suspension dims prospects for an early rollout amid some reports that the United States was aiming for an October or November delivery.
A number of South American countries, including Euador, Peru and Colombia, had been in discussions with AstraZeneca about a purchase and distribution partnership once a vaccine has been approved for public use.
The British drugmaker said it voluntarily paused trials to allow an independent committee to review safety data, and it was working to expedite the review to minimize any potential impact on the trial timeline. The first report from AstraZeneca was that one trial participant had experienced a “serious” adverse reaction to the vaccine and later information suggested there was more than one adverse case.
“This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials,” the company said in an emailed statement.
The nature of the illness or illnesses was not disclosed, although the participants are expected to recover, according to Stat News, which first reported the suspension due to a “suspected serious adverse reaction”.
The U.S. Food and Drug Administration defines an adverse event as one in which evidence suggests a possible relationship to the drug being tested.
According to a New York Times report which cited a person familiar with the situation, a participant based in the United Kingdom was found to have transverse myelitis, an inflammatory syndrome that affects the spinal cord and is often sparked by viral infections.
Whether the illness was directly linked to AstraZeneca’s vaccine remains unclear, the report said. AstraZeneca declined to comment on the report.
AstraZeneca’s shares fell more than 8% in after-hours U.S. trading, while shares in rival vaccine developer Moderna Inc rose more than 4%. Shares in AstraZeneca’s Indian unit, AstraZeneca Pharma India Ltd, tumbled more than 12%.
Called AZD1222, the vaccine is in late-stage clinical trials in the United States, Britain, Argentina, Uruguay, Brazil and South Africa and additional trials are planned in Japan and Russia. The trials aim to enroll up to 50,000 participants globally.
South Korea said on Wednesday it would look into the suspension and review its plan to participate in the manufacturing of the vaccine. “It’s not rare that clinical trials get suspended as various factors interact,” health ministry official Yoon Tae-ho told a briefing.
The decision to put the trial on hold has impacted clinical trials being conducted by other vaccine makers, which are looking for signs of similar reactions, Stat said.
The U.S. National Institutes of Health, which is providing funding for AstraZeneca’s trial, declined to comment.