Britain's health minister Matt Hancock said on Tuesday that under the "best-case scenario" a COVID-19 vaccine will be ready for Christmas.
Answering questions from the UK parliament's science and technology committee, Hancock described himself as "an optimist in life", adding that "on the best-case scenario, the answer (on whether a vaccine would be rolled out for Christmas) is yes."
It comes after scientists at the University of Oxford revealed on Monday that a vaccine under development had produced "good immune response in almost everybody".
"Vaccines are an uncertain science, and we need to be cautious," Hancock said, promising to "throw everything" at the vaccine being trialled so that it can be rolled out as quickly as possible.
"We're working really hard on this but I can't promise to play Santa," he cautioned. "We'll only recommend a vaccine when we know that it is clinically safe."
Hancock also pledged to make the vaccine available to other countries: "Our approach on the vaccine is to be global citizens".
"The point of the vaccine is that once you've got the blueprint, lots of people around the world can manufacture it and we don't want to stand in the way of that," he said.
The health official said however that the priority for the government is "controlling the virus and preparing for winter".
Measures to do so include the expansion of trace and test and capacity at NHS hospitals — including Nightingale one — and private clinics, he said.
Authorities are also working to strengthen the supply of personal protection equipment and drugs to face a possible resurgence of the deadly virus.
"We don't rule out bringing a national lockdown if that is needed," he stressed.
He defended the British government's handling of the crisis, arguing that authorities acted on the latest scientific advice with "unbelievable speed and urgency."
"We've learnt a huge amount of lessons in how we're preparing for the future," he added.
He was also once again forced to defend his recent comment that the UK entered lockdown on March 16 after being accused of revisionism. Prime Minister Boris Johnson only urged people to stay at home in a televised address on March 23.
He said that the government issued social distancing "recommendations" on March 16 which led to the amount of social activity and interaction falling.
The UK is Europe's worst-hit country with more than 45,300 fatalities and nearly 297,000 confirmed cases recorded since the beginning of the outbreak, according to a tally by Johns Hopkins University.
The government has however called for an urgent review of the way death statistics have been reported in England and Wales after it emerged that Public Health England (PHE) includes deaths of people who once tested positive but later died of other causes.
On this issue, Hancock affirmed that PHE will publish a revised methodology "very quickly" in order to "get an accurate measure for deaths with COVID."
But he added that excess mortality figures — which calculates the difference in the number of deaths over a similar period of time across multiple years —will provide the "only true measure of the impact of this in terms of mortality."