A pause in trials of a Covid-19 vaccine being developed by AstraZeneca and Oxford University underlines the importance of such tests being carried out properly, an expert has said.

Wellcome Trust director and Sage member Professor Sir Jeremy Farrar said the public must have “absolute trust” that any vaccine is safe and effective.

His comments came after AstraZeneca said the late-stage studies of the vaccine have been paused owing to a reported side-effect in a patient in the UK.

Prof Farrar told BBC Radio 4’s Today programme on Wednesday that putting a trial on hold is a common occurrence but each one must be taken seriously.

“There are often pauses in vaccine trials,” he said.

“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.

“Yes, they do happen quite commonly in vaccine trials when you’re offering a vaccine to tens of thousands of individuals, but each one must be taken seriously.”

The Government’s chief scientific adviser, Sir Patrick Vallance, told a Downing Street press conference what has happened in the Oxford trial is not unusual.

He added that similar events should also be expected in some of the other vaccine candidate trials.

But he said that overall there is positive news on vaccine and therapeutics.

Sir Patrick said: “So vaccines are progressing – some will read out this year in terms of efficacy and safety.

“And I think there’s a reasonable chance that therefore, we can think about the possibility of vaccination next year sometime at larger levels, and that is pretty much what we thought of beginning and that remains the case.”

News site Stat first reported the pause in testing and said the possible side-effect occurred in a testing volunteer in Britain, who was expected to recover.

The public must have absolute trust that these vaccines are safe and of course effective

The vaccine, developed by Oxford University, is being tested in thousands of people in Britain and the US, and in smaller study groups in Brazil and South America.

Prof Farrar said it is inevitable that some of the 30,000 to 40,000 people given the vaccine will have illnesses unrelated to it.

But he said it is crucial data is shared “transparently and openly”, and added: “In the end the public must have absolute trust that these vaccines are safe and of course effective, and in the end will hopefully bring the pandemic to a close.”

Health Secretary Matt Hancock said the Oxford vaccine trial had already overcome one such delay.

Asked on Sky News if the new pause is a setback, Mr Hancock said: “Not necessarily – it depends on what they find when they do the investigation.

“There was a pause earlier in the summer and that was resolved without a problem.”

An AstraZeneca spokeswoman said the pause is part of a standard review process which occurs if there is a “potentially unexplained illness” reported in any trial subject.

“As part of the ongoing randomised, controlled global trials of the Oxford coronavirus vaccine, our standard review process was triggered and we voluntarily paused vaccination to allow review of safety data by an independent committee,” the spokeswoman said in a statement.

“This is 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.

“In large trials illnesses will happen by chance but must be independently reviewed to check this carefully.”

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No details about the patient or the nature of the side-effect were given.

But the New York Times reported the patient had been diagnosed with transverse myelitis, an inflammatory syndrome which affects the spinal cord and is often sparked by viral infections.

Temporary holds on large medical studies are not uncommon, and looking into any unexpected reactions is a mandatory part of safety testing.

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

Two other vaccines are in huge, final-stage tests in the United States, one made by Moderna Inc and the other by Pfizer and Germany’s BioNTech.

Despite some figures, such as US President Donald Trump, insisting a vaccine will be ready in a matter of months, Oxford University has said a vaccine might not be ready before 2022.