Pharmaceutical companies running clinical trials for two high-profile coronavirus vaccine candidates announced on Friday that the trials would resume, after safety investigations found that serious illnesses in volunteers did not appear to be related to the vaccines.
The FDA authorized AstraZeneca to resume its trial after a six-week pause spurred by a neurological illness in a trial participant. Johnson & Johnson's trial was paused earlier this month.
Study pauses are not unusual in clinical trials. Unexpected illnesses are expected in trials that involve large numbers of patients, and safety investigations are necessary to determine whether the illnesses are linked to the vaccine.
“The restart of clinical trials across the world is great news as it allows us to continue our efforts to develop this vaccine to help defeat this terrible pandemic," AstraZeneca CEO Pascal Soriot said in a statement. "We should be reassured by the care taken by independent regulators to protect the public and ensure the vaccine is safe before it is approved for use."
AstraZeneca's trial, which is being conducted in a partnership with the University of Oxford in the UK, has been halted twice. The first pause occurred after a patient in July developed multiple sclerosis, which was determined to be unrelated to the vaccine. The trial was paused again in September after a participant developed a neurological illness called transverse myelitis. Trials quickly resumed in the UK, Brazil, South Africa, and Japan, while the US arm of the trial remained in limbo for weeks.
It's still unclear why the US safety investigation took so long. According to the New York Times, the FDA has now advised the company to alert trial participants about symptoms like weakness and numbness that could indicate a mild case of transverse myelitis.
Asked about the update, an AstraZeneca spokesperson stressed that the FDA had concluded it was safe to resume the trial. "Following the FDA review, we have made changes to the Informed Consent Form, which reflects the outcome of their review and is intended to provide study participants with updated information about participating in the trial," the spokesperson said.
The FDA did not respond to a request for comment.
"You want this to happen. You want people to be careful as they move forward," Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, who sits on the FDA vaccine advisory committee, told BuzzFeed News. "I think it's an abundance of caution."
"In some ways, you may be scaring people unnecessarily, or you might be informing them about something that could be a bigger problem," Offit added. "You don’t know. But in fairness, you have to let people know that it might be a problem."
Johnson & Johnson's trial, which is being tested in 60,000 participants, paused earlier this month.
"After a thorough evaluation of a serious medical event experienced by one study participant, no clear cause has been identified," the company said in a statement. "There are many possible factors that could have caused the event. Based on the information gathered to date and the input of independent experts, the Company has found no evidence that the vaccine candidate caused the event."
Offit stressed that a lot was still unknown about both of the cases. AstraZeneca's pause was only reported publicly after a private call with investors was leaked to the science publication Stat. Scientists have called for greater transparency from pharmaceutical companies as they move at breakneck speed to test a vaccine, and as public trust in the vaccines continues to drop.
"There's a lot we don't know," Offit said, urging that it would be helpful to know more about what the companies found during their safety investigations. "We just read the tea leaves here."
Both AstraZeneca and Johnson & Johnson's vaccines use the same technology to work. A harmless chimpanzee adenovirus, which typically causes harmless colds, is used to shuttle a coronavirus gene into human cells to spur an immune response. The approach has yet to lead to an approved vaccine, but it has been tested in experimental vaccines against other viruses, including influenza and Ebola.
In reality, no vaccine candidates have yet made it through their late-stage trials. An FDA science advisory committee about vaccine development on Thursday recommended that the agency collect more safety data on the vaccine candidates before authorizing them for emergency approval, a step that would further delay the availability of a vaccine.
This story has been updated to include comments from an AstraZeneca spokesperson.
This story has been updated to include comments from Paul Offit.