Researchers in the UK are not able to agree on when they think a coronavirus vaccine will be available, but they seem optimistic one will be developed.
A University of Oxford team is currently testing a vaccine candidate in humans, while another group from Imperial College London are expected to start human trials next month.
If Oxford's Covid-19 vaccine candidate proves successful, then up to 30m doses for the UK could be available by September, the government has said.
However, Professor Robin Shattock, head of mucosal infection and immunity at Imperial College London, said he thought a vaccine was not likely to be widely available until next year.
He told BBC Radio 4's Today programme: "I think we have a very high chance of seeing a number of vaccines that work because we know a lot about this target and I think there's good scientific rationale to say it's not such a hard target as others.
"My gut feeling is we will start to see a number of candidates coming through with good evidence early towards next year - possibly something this year - but they won't be readily available for wide scale use into the beginning of next year as the kind of most optimistic estimation."
Prof Shattock explained there is a difference between having the systems in place to produce a vaccine once one is developed, and having the data that proves the vaccine actually works.
He said: "It is important not to have a false expectation that it's just around the corner. It may be longer than any of us would want to think.
"There could be some success, we could see some things working earlier if we get the numbers and the AstraZeneca approach is preparing for that success."
Oxford have signed a global licensing agreement with AstraZeneca which could see it supply 100m doses - with 30m going to the UK - as soon as September, if one has been found by then.
Health Secretary Matt Hancock said that if successful, the first 30m vaccines will be "at the start for the most vulnerable".
He told MPs: "I am delighted we have been able to come to an agreement with AstraZeneca that will ensure that if the science behind the Oxford vaccine works, then we have agreement to make sure that 100m doses are available for the UK, the first 30m of which will be right at the start for the most vulnerable.
"That is a UK-wide policy, we'll deliver it right across these islands."