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On Tuesday, AstraZeneca PLC, which has been developing a vaccine with Oxford University, temporarily put its late-stage study on hold while it investigates whether a recipient’s “potentially unexplained” illness is a side effect of the vaccine.
Hancock told Sky News on Wednesday that the temporary pause is "obviously a challenge to this particular vaccine trial," but it is not the first time this has happened.
"It’s a standard process in clinical trials whenever they find something that they need to investigate," he said.
The development of the vaccine isn't necessarily impeded because of the investigation, Hancock said.
"It depends on what they find when they do the investigation," he said.
Late last month, AstraZeneca began recruiting 30,000 people in the United States for its largest study of the vaccine. It also is testing the vaccine, developed by Oxford University, in thousands of people in Britain, and in smaller studies in Brazil and South Africa.
An AstraZeneca spokesperson confirmed the pause in vaccinations covers studies in the U.S. and other countries.
In a statement issued Tuesday evening, the company said its “standard review process triggered a pause to vaccination to allow review of safety data.”
"This is 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," AstraZeneca said. "In large trials, illnesses will happen by chance but must be independently reviewed to check this carefully."
Health experts say temporary holds of large medical studies aren’t unusual and investigating any serious or unexpected reaction is a mandatory part of safety testing.
Dr. Scott Atlas, an adviser on President Trump's coronavirus task force, defended AstraZeneca's move Wednesday, telling Maria Bartiromo that this pause "is an indication that the trials are being done safely."
"This is not anything really unexpected," he said. "As they said, it's routine and these are investigated."
Atlas also said that this isn't something to be alarmed about and that this is exactly why we are doing the trials in the first place.
"People should be assured by this," he said.
However, he did note that pauses like this are the reason why "we can't totally predict exactly when things will be available."
During the third and final stage of testing, researchers look for any signs of possible side effects that may have gone undetected in earlier patient research. Because of their large size, the studies are considered the most important study phase for picking up less common side effects and establishing safety.
AstraZeneca said it's working to expedite the review of the "potentially unexplained illness" in an effort to limit any potential impact on the trial timeline.
"We are committed to the safety of our participants and the highest standards of conduct in our trials," the company said.
The development came around the same time that AstraZeneca and eight other drugmakers issued an unusual pledge, vowing to uphold the highest ethical and scientific standards in developing their vaccines.
The Associated Press contributed to this report.