Drug companies GSK and Sanofi have said they are starting clinical trials of their coronavirus vaccine.
The two firms said 440 adults would be given the vaccine at 11 sites in the US.
They hope to have the first results of the trial by December and if it is successful they will move on to further trials by the end of the year.
They join around 20 pharmaceutical companies holding clinical trials in the race to find a vaccine.
The partnership between the UK's GSK and France's Sanofi uses the same protein-based technology as one of Sanofi's seasonal influenza vaccines.
"The initiation of our clinical study is an important step and brings us closer to a potential vaccine which could help defeat Covid-19", said Thomas Triomphe, executive vice president and global head of Sanofi Pasteur.
"Our dedicated teams and partner continue to work around the clock as we aim to deliver first results in early December. Positive data will enable a prompt start of the pivotal phase 3 trial by the end of this year".
If the third stage trial goes ahead and enough data are collected, the companies plan to apply for regulatory approval in the first half of 2021.
Earlier this week, pharmaceutical company AstraZeneca, which is holding advanced clinical trials for the vaccine it is developing with Oxford University, announced it had made a deal with Oxford Biomedica to reserve production lines at the company's new manufacturing plant.
The UK government has ordered 100 million doses of the AstraZeneca vaccine, which is one of around 23 vaccines in clinical trials globally.
It is not yet known which of these experimental vaccines will work.