Clinical trials for the Oxford coronavirus vaccine may have gathered enough safety and efficacy data by the end of the year, a leading scientist has said.

Professor Andrew Pollard, director of the Oxford Vaccine Group, said it is “just possible” that there may be enough clinical trial data on Oxford University’s Covid-19 vaccine to put before regulators this year.

His comments came after England’s chief medical officer, Professor Chris Whitty, said a vaccine for coronavirus may not be ready until next winter.

Prof Pollard told BBC Radio 4’s Today programme: “I think that Chris Whitty is quite rightly being cautious, that it could take as long as that to first of all demonstrate a vaccine works and is safe and then to go through the processes of regulators looking at that very carefully to make sure everything’s been done correctly.

“But it is also just possible that, if the cases accrue rapidly in the clinical trials, that we could have that data to put before regulators this year, and then there would be a process that they go through in order to make a full assessment of the data.”

Having 20,000 people in our trials already means that that period of time will be shorter, but unfortunately I can't quite predict the future about how many cases are going to occur

Asked about the timing of a possible vaccine, he said: “That depends very much on the number of cases that occur in the weeks and months ahead.

“Even with 1,000 people eventually you’ll have enough information to know whether or not a vaccine works, but that could take years. So, having 20,000 people in our trials already means that that period of time will be shorter, but unfortunately I can’t quite predict the future about how many cases are going to occur.”

Prof Pollard said he hoped that 50,000 people would be involved in the clinical trial for the Oxford University Covid-19 vaccine candidate.

But he stressed that the size of the trial “isn’t really the issue”, adding: “What you need is to have enough cases accruing during the time of observation in the trials.”

“The size of the trial is critical, first of all for safety – so you want to have good evidence that, after a large number of people have been vaccinated, you’ve got good evidence or safety around the vaccine.

“And, secondly, you want to be able to show whether the vaccine works, and the size of the trial actually is determined largely by what the attack rate of the disease is in the study population.

“And so, if you’ve got a very, very rare disease, you need an enormous trial size, in order to be able to show whether the vaccine works. But in a situation like that at the moment coronavirus, depending on which region or country you are in, the size of the trial could be smaller or bigger just depending on how many cases are happening in that community at the time.”

He added: “There are a number of trials that we’re running from Oxford here in the UK, in Brazil, and also in South Africa, and the combined size of those three trials together is around about 20,000 people, and AstraZeneca are moving forwards in their trials in the US, hoping to start enrolling 30,000 people.

“So within the trials of the vaccine that was developed here at Oxford University, we’d expect to have perhaps 50,000 or more people in the trials in total.”

On reports that the US is planning emergency authorisation for the Oxford Covid-19 vaccine, he said: “Emergency use authorisations are well established by regulators both in the United States and in Europe; in fact, you may be aware just this week, the FDA (the US Food and Drug Administration) has granted emergency use authorisation for plasma therapy.

“So the process of going through emergency use authorisation in an emergency is well established but it still involves having carefully conducted data, just as we are collecting information about the vaccines in clinical trials that are conducted rigorously and evidence that it actually works.

“And so, for our suite of trials that we’re running from Oxford, we would expect to first of all have safety data and then evidence that the vaccine actually works.

“And before anything were to progress from there and of course it’d be AstraZeneca who would then take that forward to regulators.”