AstraZeneca, the company developing the vaccine with researchers at the University of Oxford, said Tuesday it had suspended late-stage trials to allow an independent committee to review the safety data.
The break was announced after a volunteer began to suffer from neurological symptoms associated with a rare spinal inflammatory disorder called transverse myelitis.
The drugmaker said in a statement that trials have been “voluntarily” suspended, describing them as a “routine action” that will be investigated to ensure “trial integrity” is maintained.
AstraZeneca CEO Pascal Soriot said in a private conference call with investors on Wednesday that the participant who fell ill did not yet have a confirmed diagnosis but was improving and was about to be discharged from hospital as soon as last night.
Transverse myelitis is inflammation on both sides of a section of the spinal cord and can be triggered by viral infections. This can cause pain, muscle weakness, and sensory issues.
People who have the condition usually recover within a few weeks and are often treatable with steroids, but sometimes it can persist for months, according to the Mayo Clinic.
According to the health industry news site Stat, who first reported discontinuation of the trials, Mr. Soriot also confirmed that the clinical trial was discontinued once in July after a participant experienced neurological symptoms and was diagnosed with multiple sclerosis.
The participant’s condition was deemed unrelated to the vaccine treatment, he said.
The trial has been suspended in the UK, Brazil, South Africa and the US, sparking nervousness around the development of a vaccine against a pandemic that has brought much of the world to its knees.
Scientists said such breaks were not uncommon, but warned that every break should be taken seriously.
Sir Jeremy Farrar, director of the Wellcome Trust and member of Sage, told BBC Radio 4 Today program: “For me, this underlines how important it is that these vaccine trials are carried out correctly, that they have independent oversight, that the regulator is involved and that we can trust and support this regulator and that we take these kinds of breaks seriously. “
Health Secretary Matt Hancock also sought to allay concerns about the break and stressed that clinical trials are often halted “whenever they find something they need to investigate.”