Studies of the final phases of AstraZeneca’s candidate vaccine for Covid-19 are temporarily suspended while the company investigates whether a patient suffered a serious side effect or if their discomfort is not linked to the inoculation.
In a statement issued Tuesday night, the company said its “standard review process created a pause in vaccinations to allow review of safety data.”
AstraZeneca did not disclose any information about the possible side effect, other than calling it “a potentially unexplained illness.” The STAT news portal was the first to report the pause in testing, claiming that the possible side effect occurred in the UK.
A spokesperson for AstraZeneca confirmed that the pause in vaccinations covers studies in the United States and other countries. Late last month, AstraZeneca began recruiting 30,000 people in the United States for its largest trial of the vaccine. It is also testing the vaccine – developed by the University of Oxford – in thousands of people in Britain and in smaller-scale studies in Brazil and South Africa.
Two other vaccines are in the final stages of testing in the United States: one produced by Moderna Inc. and the other by Pfizer and the German laboratory BioNTech. Those two vaccines work differently than AstraZeneca’s, and the studies have already recruited two-thirds of the volunteers in need.
Temporary pauses in large-scale medical studies are not unusual, and investigating any possible serious side effects or unexpected reactions is mandatory. AstraZeneca pointed out that the problem could be a coincidence, as diseases of all kinds can arise during studies of thousands of people.
“We are working to expedite the review of that lone event to minimize any potential impact on the testing schedule,” the company said in its statement.
The unexplained illness was likely severe enough to require hospitalization and not a mild side effect like fever or muscle pain, said Deborah Fuller, a University of Washington researcher working on another Covid-19 vaccine. and that has not yet begun to be tested in people.
“This is not something to be alarmed about,” Fuller said. Instead, he added, it’s reassuring that the company is pausing the study to find out what’s going on and carefully monitoring the health of the study participants.
Dr. Ashish Jha of Brown University tweeted that the meaning of the pause was unclear, but said he remained “optimistic” that an effective vaccine would be found in the coming months.
“But optimism is not a test,” he wrote, before adding: “Let science guide this process.”
Angela Rasmussen, a virologist at Columbia University in New York, tweeted that the disease may not be related to the vaccine, “but the important part is that this is why we do tests before releasing a vaccine to the general population.”
During the third and final stage of a trial, researchers look for any signs of possible side effects that have not been detected in previous research with patients. Due to their large size, studies are considered the most important phase to detect less common side effects and ensure safety.
The trials also assess effectiveness by tracking who gets sick and who doesn’t among patients receiving the vaccine and those receiving a placebo injection.
The announcement came on the same day that AstraZeneca and eight other pharmaceutical companies pledged to uphold the highest ethical and scientific standards in the development of their vaccines.
That came amid fears that President Donald Trump will pressure the Food and Drug Administration (FDA) to approve a vaccine before it is shown to be safe and effective.
The United States has invested billions of dollars to rapidly develop a coronavirus vaccine, but public fears that a vaccine will be ineffective and unsafe could prove disastrous and derail efforts to vaccinate millions of Americans.
Representatives for the FDA did not immediately respond to requests for comment.