Late-stage coronavirus vaccine trials run by AstraZeneca and Johnson & Johnson have resumed in the United States after the companies said Friday that serious illnesses in a few volunteers appeared not to be related to the vaccines.
Federal health regulators gave AstraZeneca the green light after a six-week pause, concluding there was no evidence that the experimental vaccine had directly caused the neurological side effects reported in two participants.
Johnson & Johnson said that its trial, which had been on pause for 11 days, would restart after learning that a “serious medical event” in one study volunteer had “no clear cause.”
A Food and Drug Administration spokesperson declined to comment on the trial restarts.
AstraZeneca and Johnson & Johnson are two of the four companies in late-stage clinical trials in the United States for experimental coronavirus vaccines. Their two high-profile competitors, Moderna and Pfizer, are also in advanced trials.
AstraZeneca moved swiftly into clinical trials, enrolling thousands of volunteers for its vaccine trials around the world. But all of the trials were halted September 6. A volunteer who had received the vaccine in the United Kingdom reportedly experienced symptoms of transverse myelitis, or inflammation of the spinal cord, triggering a global pause to the company’s efforts.
The incident drew some concern among experts, who noted that a similar adverse neurological event, reported months ago, had occurred in another vaccinated volunteer. Although this earlier event prompted its own pause in AstraZeneca’s trials, an independent safety board ultimately determined it was unrelated to the vaccine, allowing studies to resume.
After the second AstraZeneca halt in September, trials abroad rapidly restarted in most countries. But the US hiatus persisted, with few details released as to why.
Johnson & Johnson started its Phase 3 trial on 60,000 volunteers in September. On October 12, the company announced its own trial pause, citing concerns that an illness had happened in one of its volunteers as well. The company has kept mostly quiet about the details of the incident.
“There are many possible factors that could have caused the event,” the company said. “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.”