There is no assumption a coronavirus vaccine will be available in the immediate future, MPs have heard.

Sir Patrick Vallance, the Government’s chief scientific adviser, said the UK is looking at a number of options because it is not yet known which Covid-19 vaccine candidate will be effective.

His comments come as reports suggest the University of Oxford’s human trials of a potential vaccine are reported to have shown promising results.

Results of the trial are expected to be published next week.

Our assumption is we won’t have it and when we get it we will be thrilled

Sir Patrick told the Science and Technology Committee the UK had a “wide range” of vaccine options “because we don’t know which one is going to win”.

He said: “Our assumption is we won’t have it and when we get it we will be thrilled.”

Across the world dozens of vaccines are in clinical trials, while more than 100 are in development.

Some scientists are calling for people to be deliberately exposed to Covid-19 once they have been injected with the vaccine, a process known as challenge trials.

A number of prominent scientists, including Nobel laureates, have signed an open letter to the head of the US National Institutes of Health (NIH), from the 1 Day Sooner organisation, arguing this should not be left to chance

They say these challenge trials could accelerate vaccine development.

The signatories, who include Adrian Hill, director of the Jenner Institute at Oxford where the vaccine was developed, are calling in the NIH, its allies, international funders, and world bodies like the World Health Organisation, to undertake immediate preparations for human challenge trials.

Prof Hill said “collaborative human challenge studies should be feasible and informative in the coming months”.

The only way of knowing if any of the vaccines works is if enough volunteers are subsequently exposed to coronavirus in their daily life and do not get infected.

But with transmission rates falling in the UK that could take a long time.

Asked about human challenge trials, Sir Patrick said the method was a “well-established way” of testing vaccines.

He added: “What are the two big challenges for this virus?

“Dose and rescue.

“So the prerequisites to do human challenge studies are to understand what dose causes a safe infection and can you rescue it if you get it wrong?”

Asked what the current answer to those questions was, he said: “We don’t know the dose and we don’t yet know when remdesivir (drug) will rescue the infection.

“It is absolutely the right thing to explore, but we are not there yet in terms of having all the answers.

“We need to make sure we progress safely.”