Oxford University’s clinical trials for a coronavirus vaccine have been suspended after a participant fell ill with an “unexplained illness”.

A potential vaccine for COVID-19 is being jointly developed in the UK by Oxford University and the British-Swedish pharmaceuticals company AstraZeneca, but all testing has been temporarily stopped following news that a participant has fallen seriously ill.

The New York Times has reported that a volunteer had contracted transverse myelitis, a neurological condition where the spinal cord becomes inflamed. However, AstraZeneca has not commented on the claim and an independent inquiry will determine if it was the vaccine that caused the participant’s illness.

Dr Anthony Fauci, lead adviser of the White House Coronavirus Task Force, has called the news “unfortunate”, but an AstraZeneca spokesperson has described the pause as “routine”. A similar incident had occurred earlier in the clinical trial and it is widely expected that trials will resume shortly.

According to The Guardian, approximately 17,000 people in the UK, South Africa and Brazil have so far participated in trials for the Oxford vaccine, which is now in Phase 3 of testing. The initial Phase 1 and Phase 2 clinical trials had been successful and generated a “strong immune response” in participants. Phase 3 trials, led by AstraZeneca, began in the United States this summer as President Trump pushes for the development of a vaccine by the time of the presidential election in November.

On Tuesday, AstraZeneca, along with 9 other companies including Johnson & Johnson, signed up to a pledge to uphold scientific and ethical standards during their quest for a coronavirus vaccine.

The UK Health Secretary, Matt Hancock, told LBC Radio on Monday that it is “most likely” that a vaccine will be ready in the early months of 2021 and that the UK has signed a contract with AstraZeneca for 30 million doses.

The news about Oxford’s vaccine comes amid rising coronavirus cases across the UK and widespread debate about the health risks involved in students returning to UK universities over the coming weeks.