A coronavirus vaccine will "realistically" not be available before Christmas, a World Health Organisation expert has said, dampening hopes it may be available before then.
Mike Ryan, head of WHO's emergencies programme, said vaccine development is being sped up as much as possible but "corners can't be cut on safety".
It comes after the head of the UK's vaccine taskforce said there is a "possibility" a coronavirus vaccine could be rolled out by Christmas.
Noting that several vaccines are now in phase three trials and none have failed so far, Dr Ryan admitted "we are seeing hopeful signs".
"But I think we have to be realistic on two things," Dr Ryan warned.
"One, we need to be realistic on time. No matter how hard we push, we have to make sure these vaccines are safe and that they are effective, and that takes its own time, and we are speeding that up as much as possible.
"But we are not in any way going to cut corners on safety."
He confirmed: "Realistically it's going to be the first part of next year before we start seeing people getting vaccinated."
Dr Ryan also warned that vaccines are not 100 per cent effective and called for people to be "realistic in our expectations".
"We have to wait and see how effective the vaccine is going to be and how long the protection will last," he said.
"The idea we are going to have a vaccine in two or three months and then all of sudden this virus is going to go away - I would love to be here saying that to you.
"But that's just not realistic and it's really important that we are realistic in our expectations."
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Dr Ryan, speaking alongside Dr Maria Van Kerkhove on Wednesday, urged people to "do what we can now", which includes hand washing, social distancing and wearing face masks.
"We have to push and get the best vaccines we can and the best treatments we can, but we also need to be realistic and do what we can now," he said.
"There is so much we can do now, and it will be so much easier to get rid of this virus using a vaccine if we have already suppressed it."
The news comes after a coronavirus vaccine being developed by Oxford University scientists was found to be "safe and induce an immune response".
The team of experts, led by Professor Sarah Gilbert, will now race to get more widespread community trials carried out in the UK and abroad, with the hope of completing them by the autumn.
Dr Ryan thanked volunteers who have stepped forward to take part in vaccine trials.
"The real world trials are very different and we really thank those people who are volunteering for the studies," he said.
"They are hugely important studies and people are stepping forward and saying 'yes, I want to be part of this study'.
"It's a massive contribution to the whole world. It's a huge gift to humanity."