“Globally some 18,000 individuals have received study vaccines as part of the trial. In large trials such as this, it is expected that some participants will become unwell and every case must be carefully evaluated to ensure careful assessment of safety,” the University of Oxford said in a statement.
AstraZeneca released a statement that it was working with global health authorities to “be guided as to when other clinical trials can resume,” including the 30,000-person trial in the United States that began in late August.
The temporary hold on the trial because of a single illness was seen by many experts as evidence that systems in place to protect patient safety are functioning properly. National Institutes of Health Director Francis S. Collins testified before Congress that the illness that stopped the trial was transverse myelitis, an inflammation of the spinal cord, but the diagnosis was not confirmed by the drug company or by Oxford researchers.
Transverse myelitis is a rare, treatable condition. It can occur in patients with multiple sclerosis but can also be “idiopathic,” the medical term for a condition that has no clear cause. Years of investigation to try to understand if it could be triggered by vaccinations have never shown a clear link.
“It can be very difficult, if not impossible, to ever conclusively prove what a trigger was for idiopathic transverse myelitis,” said Benjamin Greenberg, a neurologist at the University of Texas Southwestern Medical Center who treats the condition.
With hundreds of millions of vaccinations given each year, Greenberg said, people inevitably — and by coincidence — fall sick in the days or weeks after receiving the inoculation. A person may have a heart attack the day after taking an aspirin, for example, but it doesn’t mean the medication caused the event. The important thing is to study whether it’s likely that a vaccine triggered any adverse event, Greenberg said.
Greenberg said in an interview a day before the trial resumed that safety guardrails appeared to be working in the vaccine trial.
“It’s nice to see the system worked in terms of vaccine development … the study being put on hold out of an abundance of caution, despite the fact there are enormous pressures to get a vaccine developed and available,” Greenberg said. “Everybody did what they are supposed to — that was very reassuring.”