Coronavirus vaccine: Why has Oxford AstraZeneca trial been paused?

The leading vaccine candidate trial is being suspended after a participant fell ill

AstraZeneca has suspended its coronavirus vaccine trial after a participant became ill, leading the pharmaceutical company to investigate whether the reported side effect is directly connected to the experimental vaccine candidate.

The pause in the leading vaccine trial “underlines the importance of it being carried out properly”, the director of the Wellcome Trust and member of Sage has said, echoing the World Health Organisation’s message about prioritising vaccine safety. 

But it remains unclear how long the halt will last – how will this affect the search for the vaccine?

Why have the trials been suspended?

In a written statement, AstraZeneca said the suspension was a “routine action which has to happen whenever there is a potentially unexplained illness in one of the trials, while it is investigated, ensuring we maintain the integrity of the trials”.

The drug manufacturer said illnesses do happen by chance in large trials but these occurrences "must be independently reviewed to check this carefully".

AstraZeneca did not disclose the nature of the participant’s illness, but the New York Times reported a source close to the trial as saying the volunteer was based in the UK and had developed transverse myelitis, an inflammatory syndrome that affects the spinal cord and can be caused by viral infections.

It is not clear if the participant’s diagnosis is directly connected to the experimental vaccine.

How common is this?

Speaking on BBC Radio 4’s Today programme, the director of the Wellcome Trust and member of Sage Sir Jeremy Farrar said that while trials are often suspended, each pause must be taken seriously and the reason for it independently examined.

"For me it underlines just how important it is that these vaccine trials are done properly, that they have independent oversight, that the regulator is involved and we can trust and support that regulator and that we take these sorts of pauses seriously.” 

The health secretary, Matt Hancock, also stressed that clinical trials are often halted, telling Sky News that it is “a standard process in clinical trials whenever they find something that they need to investigate”.

What happens next?

AstraZeneca said it had voluntarily paused the trial to allow review of safety data by an independent committee to take place.

The pharmaceutical company added that it is working to expedite the review of the single event to minimise any potential impact on the trial timeline, and is committed to the safety of our participants.

Will the halt delay the vaccine?

The health secretary said it wouldn’t “necessarily” set back attempts to find a vaccine, saying "it depends on what they find when they do the investigation”.

Mr Hancock said the Oxford vaccine trial had been paused earlier in the year.

He added: "There was a pause earlier in the summer and that was resolved without a problem."

It is not clear how long AstraZeneca’s halt will last.

What does the WHO say?

 The UK drugmaker’s vaccine candidate, developed with the University of Oxford, was in late-stage trials and had previously been described as the most advanced coronavirus vaccine candidate by the WHO.

The global body also stressed the importance of prioritising vaccine safety in light of the development.

“Just because we talk about speed… it doesn’t mean we start compromising or cutting corners on what would normally be assessed,” Dr Soumya Swaminathan, the WHO’s chief scientist, said.

“The process still has to follow the rule of the game. For drugs and vaccines which are given to people, you have to test their safety, first and foremost,” Dr  Swaminathan added.