Johnson & Johnson has launched a late-stage trial in Britain to test a two-dose regimen of its experimental COVID-19 vaccine among thousands of volunteers.
In expanding its trials by geography and type, the UK arm of the drugmaker's study aims to recruit 6000 participants among a total of 30,000 people globally.
Volunteers will be recruited at 17 sites and given a first dose of either a placebo or the experimental shot, currently called Ad26COV2.
That will be followed by a second dose or placebo 57 days later, said Saul Faust, a professor of paediatric immunology and infectious diseases co-leading the trial at University Hospital Southampton.
J&J signed an agreement for the two-dose global Phase III clinical trial with the British government in August, to run in parallel with a 60,000-person trial of a single shot of the experimental vaccine launched in September.
If the results of the single-shot trial are positive, the company said on Monday it could simplify distribution of millions of doses compared with leading rivals requiring two doses.
The efficacy of a double-dose vaccine could be affected if people fail to get their a second shot.
Rival drugmakers Pfizer and BioNtech said last week their potential COVID-19 shot showed more than 90 per cent efficacy in interim data from a late-stage trial, boosting hopes vaccines may be ready for use soon.
While the Pfizer-BioNtech vaccine uses a new technology known as messenger RNA, J&J's uses a cold virus to deliver genetic material from the coronavirus into the body to prompt an immune response.
The platform, called AdVac, is also used in an Ebola vaccine approved earlier this year.
"It's really important we pursue trials of many different vaccines from many different manufacturers and be able then to ensure the supply both to the UK and global population," Faust said.
Recruitment into the study will complete in March and the trial will last 12 months.