The pharmaceutical company AstraZeneca on Tuesday said it has paused large, late-stage global trials of its experimental coronavirus vaccine because of a serious suspected adverse reaction in a study participant, reported New York Times.
It is not yet known whether the reaction was directly caused by the company’s vaccine or was coincidental.
The pause, which was first reported by STAT, will allow AstraZeneca, a British-Swedish company, to conduct a safety review and investigate whether the vaccine caused the illness. How long the hold will last is unclear.
Drug companies are racing to complete a coronavirus vaccine that could bring an end to a pandemic that has already claimed more than 8,90,000 lives globally.
AstraZeneca is one of three front-runner companies whose vaccines are in late-stage clinical trials. The company has said it hoped to have a vaccine ready before the end of the year. If the cause of the reaction turns out to be related to the vaccine, those efforts could be derailed.
In a statement, AstraZeneca described the trial’s halt, which was instituted voluntarily, as a “routine action which has to happen whenever there is a potentially unexplained illness in one of the trials, while it is investigated, ensuring we maintain the integrity of the trials.”
The company said that in large trials like the ones it is overseeing, participants do sometimes become sick by chance “but must be independently reviewed to check this carefully.”
The company said it was “working to expedite the review of the single event to minimize any potential impact on the trial timeline,” and reaffirmed its commitment “to the safety of our participants and the highest standards of conduct in our trials.”
A person familiar with the situation, who spoke on the condition of anonymity, said that the participant who experienced the suspected adverse reaction had been enrolled in a Phase 2/3 trial based in the United Kingdom. The individual also said that a volunteer in the UK trial had received a diagnosis of transverse myelitis, an inflammatory syndrome that affects the spinal cord and is often sparked by viral infections. However, the timing of this diagnosis, and whether it was directly linked to AstraZeneca’s vaccine, is still unknown.
AstraZeneca declined to comment on the location of the participant and did not confirm the diagnosis of transverse myelitis. “The event is being investigated by an independent committee, and it is too early to conclude the specific diagnosis,” the company said.
In a paper published in The Lancet in July, researchers behind AstraZeneca’s formulation reported that the majority of participants in the vaccine’s Phase 1/2 had experienced some mild or moderate side effects, including muscle aches and chills. None of the reactions, however, were considered severe or life-threatening, and resolved quickly. The vaccine was deemed safe enough to proceed to further testing.
AstraZeneca’s vaccine is in Phase 2/3 trials in England and India, and in Phase 3 trials in Brazil, South Africa and more than 60 sites in the United States.
Phase 3 trials evaluate whether vaccine candidates protect people from infection or severe disease compared to a placebo.