AstraZeneca Halts Phase 3 Vaccine Trial Over Possible Serious Adverse Reaction

AstraZeneca has paused a late-stage trial of its promising COVID-19 vaccine candidate while it evaluates a single UK patient who may have experienced a serious adverse reaction.

The drugmaker said in a statement that its “standard review process was triggered and we voluntarily paused vaccination” in the U.S. phase 3 trial in order to assess the safety data. AZ did not elaborate on the nature of the possible adverse reaction except to describe it as “a potentially unexplained illness,” meaning it’s possible it may not have been caused by the vaccine.

The company, whose candidate is seen as one of the most likely vaccines to pan out as safe and effective, downplayed the alarming study freeze, explaining that “this is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials … [to ensure] we maintain the integrity of the trials.”

 “We are working to expedite the review of the single event to minimize any potential impact on the trial timeline,” the company said in its statement. “We are committed to the safety of our participants and the highest standards of conduct in our trials.”

The UK drugmaker, which is licensing the vaccine candidate from the University of Oxford, began the 30,000-patient U.S. phase 3 trial on Aug. 31 at 62 sites, according to ClinicalTrials.gov. The company said it expects results later in the year, but it’s unclear if this setback will significantly impact its projected timeline (DID, Sept. 1). — James Miessler