Human trials of Oxford vaccine on hold in the US over spinal-cord disease fears

Human trials of the Oxford and AstraZeneca coronavirus vaccine are yet to resume in the US over concerns the jab may cause adverse reactions.

Trials of the Oxford vaccine have been paused twice after two participants, both British women, sequentially developed "unexplained neurological symptoms".

In the second case, the condition has been reported to be transverse myelitis, an inflammation of the spinal cord that can cause paralysis, although there has been no definitive diagnosis.

The first pause, in July, was not publicly revealed and the trial was restarted after it was determined the volunteer had multiple sclerosis, a condition that can cause the same neurological reaction. The second pause was widely reported two weeks ago.

Trails of the vaccine have since been restarted in Britain, Brazil, India and South Africa, but are still on pause in the US where the legal and historical context means regulators tend to take a tougher stance.

On Saturday, AstraZeneca released further data on its trial protocols, but US experts continued to raise concerns.

Dr Peter Jay Hotez, a virologist with Baylor College of Medicine in Houston, Texas, told the New York Times: “The communication around it has been horrible and unacceptable. This is not how the American people should be hearing about this.”

Dr Hotez, whose views were echoed by other US experts, also criticised statements released by UK Government officials, including regulators, who he said had failed to supply a clear rationale for resuming their trials.

“Tell us why you came to that decision,” he was reported as saying.

In an information sheet for trail volunteers dated September 11, AstraZeneca explains the risks as follows: “Reactions in the nervous system are also extremely rare, but can include an illness called Guillain-Barré syndrome, a condition in which people can develop severe weakness and can be fatal.

“In the current trial we have undertaken safety reviews when volunteers in the trials [of the vaccine] developed unexplained neurological symptoms including changed sensation or limb weakness, and have paused the study while a safety review took place.

“After independent review, these illnesses were either considered unlikely to be associated with the vaccine or there was insufficient evidence to say for certain that the illnesses were or were not related to the vaccine.

“In each of these cases, after considering the information, the independent reviewers recommended that vaccinations should continue”.

The documentation adds that adverse neurological events events have not previously been seen in vaccines which use the same viral vector as that used in the Oxford-AstraZeneca jab.

The US Food and Drug Administration (FDA), the main drugs regulator, has not commented but is reported to be requesting further data on the two adverse reactions from AstraZeneca.

On Saturday, following calls for greater transparency, the company released related details about its trial protocols and how it will calculate if the vaccine works.

It said its goal is a vaccine with 50 per cent effectiveness, the minimum threshold for FDA approval.

To determine it had hit that target with statistical confidence, it would have to record at least 150 confirmed cases of Covid-19 among trial participants.

But once 75 cases were recorded, it added, the trial’s safety board would perform an early analysis, perhaps giving it enough data to apply for an early emergency use licence.

Concerns around neurological side-effects are especially sensitive in the US.

In 1976, an emergency influenza vaccine caused 450 cases of Guillain-Barré syndrome and 30 people died after 45 million people were vaccinated.

Guillain-Barré syndrome and transverse myelitis are closely related conditions, both causing inflammation of the spinal cord.

The fears among experts is that such conditions are relatively rare, with transverse myelitis diagnosed in only about one in 250,000 people a year, making it difficult to spot.

Dr Paul Offit, a professor at the University of Pennsylvania and a member of the FDA’s advisory committee on vaccines, told the New York Times it was unclear how AstraZeneca – or the UK regulators – determined that the second neurological reaction it reported was not related to the vaccine.

The trial in Britain involved only about 8,000 volunteers when it was reported.

Mark Slifka, a vaccine expert at Oregon Health and Science University, said: “If there are two cases, then this starts to look like a dangerous pattern. If a third case of neurological disease pops up in the vaccine group, then this vaccine may be done.”

Correction: this story has been updated to make clear there has been no definitive diagnosis of transverse myelitis. Both adverse events are formally classed as  "unexplained neurological symptoms". Such events have not previously been associated with vaccines which use the same vector as the Oxford-AstraZeneca jab.