England's chief medical officer has said it would be "foolish" to plan for winter on the basis of having a coronavirus vaccine.
But Professor Chris Whitty told reporters on Saturday that there was a "reasonable chance" there could be vaccines to the virus before the winter of 2021-2022.
He warned that going into winter there will be "real problems" with Covid-19 and said that the country should plan on the basis of no vaccine being available.
Prof Whitty added: "I would obviously be delighted if it came earlier rather than later but I'd be quite surprised if we had a highly effective vaccine ready for mass use in a large percentage of the population before the end of winter, certainly before this side of Christmas.
"Now that may be wrong, a lot of people are doing a huge amount scientifically, logistically to make sure that's a pessimistic statement, to try and see if we can get a vaccine at extraordinarily fast speed but we have to check it works and we have to make sure it's safe and these things do take time.
"So I think if we look forward a year I think the chances are much greater than if we look forward six months and we need to have that sort of timescale in mind.
"So planning for the next winter, it would be foolish to plan on the basis we will have a vaccine.
"We should plan on the basis we will not have a vaccine and then if one does prove to be effective and safe and available then we're in a strong position to be able to use it and that will be great but we should be planning on the basis of what we currently have."
I'm confident in the long-term in the ability of science to get us out of this hole but I don't think we can expect it to happen in the next few weeks or even the next few months.
But Prof Whitty said he was confident in the ability of science to help tackle the virus but it would not be in the next few weeks or months.
He added: "I'm confident in the long-term in the ability of science to get us out of this hole but I don't think we can expect it to happen in the next few weeks or even the next few months."
His comments to reporters come as he joined the UK's chief and deputy chief medical officers to issue a joint statement on schools and childcare reopening.
When asked if there were decisions he would have made differently earlier in the pandemic Prof Whitty said "of course" but plans had to be made with the information available.
He added: "There is a long list of things which, if we knew at the beginning of this what we know now about this virus, about how it operates and also how the initial epidemic started, of course we would have done differently and we knew at the time that it would be easier to plan with the huge benefit of hindsight, but you have to plan with the information you've got available to you, but yes, of course."
When asked if the country should have gone into lockdown earlier Prof Whitty said there were a "wide range of views" on that issue but it did not help with forward planning.
He added: "I'm very happy to give a long and rather tedious mathematical answer but I think in due course we'll be going through that but that's not actually something that helps us with forward planning and that's the thing which I and my colleagues are really critically concentrating on at the moment."