By Keir Simmons, Linda Givetash and Laura Saravia for NBC News

LONDON ⁠— An experimental vaccine for COVID-19 under development at Oxford University hit a milestone Friday with researchers announcing it will be progressing to advanced stages of human trials.

It will be tested in 10,260 volunteers across the United Kingdom to determine how effective it is at preventing infection, the university said in a statement. If successful, it could be on the market as early as September, according to British-Swedish drugmaker AstraZeneca, which partnered with the university in April to manufacture and distribute the vaccine.

“We’re thrilled,” Adrian Hill, one of the researchers leading the project, told NBC News.

The company agreed to produce at least 400 million doses and secured total manufacturing capacity to produce 1 billion doses by the end of 2021, with first deliveries this September.

The Oxford study is one of the many racing to find an effective and safe vaccine for the coronavirus alongside efforts to contain the spread of the pandemic.

It uses a weakened version of a common cold virus that normally causes infections in chimpanzees but has been genetically modified so it can’t replicate in humans.

The effectiveness of the vaccine is still to be determined. Earlier tests conducted in monkeys showed success in moderating the severity of the virus, but not preventing infection.

Researchers are still monitoring the first 1,000 volunteers who either received a dose or were part of the control group in the first phase of the current study to see if they develop antibodies or become infected with the coronavirus.

Government approval is now allowing researchers to move ahead with the second and third phases of testing, which will see more people across a wider age range — including older adults and children — tested. The second phase begins June 1 in the U.K. and researchers hope to launch clinical trials in the United States in the coming weeks.

Health care professionals are among the volunteers in the trial because of their exposure to the virus.

On its chances of working, Hill said, “We still think they’re fairly high but not guaranteed. But we’re doing our best to show that it works over the next few months.”

Researchers hope to have results from the thousands of new participants by the end of August.

While the trials are moving quickly, Hill said, safety has not been compromised.

Although the prospect of a vaccine provides hope for bringing an end to the pandemic, Hill added that in the meantime people should continue to heed social distancing measures.

“Nobody really wants to get infected with this virus and there are lots of things you can do to reduce your chances of that,” he added.Keir Simmons

Keir Simmons is a London-based foreign correspondent for NBC News.

Linda Givetash is a London-based producer for NBC News. Laura Saravia

Laura Saravia is a producer based in London.