UK scientists are hopeful a coronavirus vaccine could be ready as soon as September.
Sarah Gilbert, a professor of vaccinology a Oxford University, said she is "80% confident" a jab being developed by her team will be proved effective by the autumn.
With the government potentially willing to fund millions of doses in advance - if results look positive - then it could be just months away from being available to the public.
Human trials are set to begin on the vaccine in a fortnight, making it one of the most promising efforts in the world.
If successful, Prof Gilbert's team could provide a crucial breakthrough in the battle against Covid-19.
With some medical experts fearing a relaxation of lockdown measures could lead to a fresh surge in infections, a return to normal life relies heavily on finding a vaccine that works.
Although it has been estimated this will take 18 months, Professor Gilbert has said in a best-case scenario her team could have one ready by September.
She had previously said she hoped it could be developed by the end of the year.
Prof Gilbert told The Times : "I think there's a high chance that it will work based on other things that we have done with this type of vaccine."
She added: "It's not just a hunch and as every week goes by we have more data to look at. I would go for 80 percent, that's my personal view."
However, she also warned that "nobody can promise it's going to work".
Prof Gilbert, who has been working seven days a week to put the vaccine through development stages, added her researchers will need to trial it in a country with a high rate of transmission to get quick results.
Her team is one of dozens worldwide who have been racing to find a way to immunise people against the devastating flu-like virus.
Health experts believe coronavirus mutates at a slower rate than other respiratory viruses, particularly flu.
This has led to hopes that, once a jab is widely available, it will provide protection against the highly contagious Covid-19 and any further strains which develop, for several years.
By 5pm on Friday, the UK had recorded 8,958 people had died after testing positive for Covid-19.
