Results of a human trial of a coronavirus vaccine could be available by the middle of June, an expert has said.

Professor Sir John Bell, regius professor of medicine at Oxford University, said “several hundred” people have been vaccinated and the challenge now is to be able to manufacture at scale once it is approved by the regulators.

At the end of April a team of researchers at Oxford started testing a Covid-19 vaccine in human volunteers.

Around 1,110 are expected to take part in the trial, half receiving the vaccine candidate and the other half (the control group) receiving a widely available meningitis vaccine.

Prof Bell told BBC Radio 4’s Today programme: “We also want to make sure that the rest of the world will be ready to make this vaccine at scale so that it gets to populations in developing countries, for example, where the need is very great.

“We really need a partner to do that and that partner has a big job in the UK because our manufacturing capacity in the UK for vaccines isn’t where it needs to be, and so we are going to work together with AstraZeneca to improve that considerably.”

He rejected the idea of challenge therapy – that would deliberately infect healthy volunteers with coronavirus – and said there should be results on the vaccine trial by using normal exposure to the virus, if you keep your head down.

Prof Bell said: “Well, we’ve got over 1,000 people that want to start phase 1/2 project.

“And so far so good, and we’re now starting to wait for an advocacy signal to see whether people who’ve been vaccinated, don’t get the disease so that’s the next step.”

He added that with the disease on the wane, there is a risk there may not be enough active disease to catch people.

“We’re doing those calculations because we have quite good data now on how much disease there is around,” Prof Bell said.

He also explained that the researchers had discussed deliberately exposing people to the virus, but the practicalities are complicated, as there is no treatment yet to to rescue people if they get sick.

He added that to check its effectiveness, you would need to give the virus to those most at risk, and the risk of them dying would be very high if it did not work.

I think it's a bit early to say, but we have good reason to be sufficiently optimistic that at the end of the day, some vaccines will make it

On Thursday the European Medicines Agency (EMA) said licensed drugs to treat Covid-19 could be available in the next few months, and that a vaccine might be approved in early 2021, in a “best-case scenario”.

Dr Marco Cavaleri, who heads the European regulator’s vaccines department, told a media briefing that approving medicines to treat Covid-19 might be possible “before the summer”.

Despite vaccines usually taking years to develop, Dr Cavaleri said that if some of the candidates already being tested prove to be effective, they could be licensed by early next year.

Saying that many experimental vaccines never make it to the end, he added: “But we can see the possibility that if everything goes as planned, vaccines could be approved a year from now.”

Dr Cavaleri said: “I think it’s a bit early to say, but we have good reason to be sufficiently optimistic that at the end of the day, some vaccines will make it.”

Professor Stuart Ralston, chairman of the Commission on Human Medicines, said he is sure a vaccine will be developed.

Speaking at a webinar of The Royal Society of Medicine, he said: “I’m hoping maybe the start of next year we might have something if it pans out.

“I think there will be a vaccine – I’m confident there will be a vaccine. The exact timescale I can’t be absolutely sure (about).

The comments come days after Prime Minister Boris Johnson said the development of a Covid-19 vaccine was not “guaranteed”, but the UK was at the forefront of international efforts to develop one.