AstraZeneca Plc said Tuesday that it has halted a late-stage trial of one of the main candidates for the Covid-19 vaccine after an unexplained illness in a study participant.
“Our standard review process was activated and we voluntarily stopped vaccination to allow for review of safety data by an independent committee,” company spokeswoman Michele Meixell said in an emailed statement.
The study is testing a Covid-19 vaccine being developed by researchers at AstraZeneca and the University of Oxford at various sites, including the UK, where the disease has been reported.
The nature of the case and when it happened were not detailed, although the participant is expected to recover, according to Stat News, which first reported that the trial was stopped because of a “suspected serious adverse reaction.” The United States Food and Drug Administration defines that as an adverse event in which evidence suggests a possible relationship to the drug being tested.
The suspension of the trial has affected other AstraZeneca vaccine trials, as well as clinical trials being conducted by other vaccine manufacturers, looking for signs of similar reactions, Stat said.
The U.S. National Institutes of Health, which is providing funding for the AstraZeneca trial, declined to comment.
The AstraZeneca statement said that “in large trials, diseases will happen by chance, but they need to be independently reviewed to verify this carefully.”
Shares of AstraZeneca fell more than 8% in after-hours trading in the United States, while shares of rival vaccine developers rose. Moderna Inc was up more than 4% and Pfizer Inc was up less than 1%.
Moderna, in an emailed statement, said it was “not aware of any impact” on the ongoing COVID-19 vaccine study at this time.
Nine major vaccine developers from the US and Europe pledged Tuesday to uphold scientific standards of safety and efficacy for their experimental vaccines despite the urgency to contain the coronavirus pandemic.
The companies, including AstraZeneca, Moderna and Pfizer, issued what they called a “historic compromise” after heightened concern that safety standards could fail in the face of political pressure to launch a vaccine.
The companies said they will “uphold the integrity of the scientific process as they work toward potential global regulatory filings and approvals of the first COVID-19 vaccines.”
The other signatories were Johnson & Johnson, Merck & Co, GlaxoSmithKline, Novavax Inc, Sanofi and BioNTech.
