Johnson & Johnson has said its single-dose vaccine is 66% effective in preventing Covid-19 globally.
The single-shot vaccine, which has been developed by Johnson & Johnson's pharmaceutical arm Janssen, is 66% effective overall at preventing moderate to severe Covid-19 28 days after vaccination.
It said its vaccine was 72% effective in preventing Covid-19 in the United States but a lower rate of 66% was observed globally in the large trial conducted across three continents and against multiple variants.
The firm said the jab was 85% effective in preventing severe disease "and demonstrated complete protection against Covid-19-related hospitalisation and death as of day 28".
It said the jab worked across multiple variants of coronavirus, including the South African variant which has been worrying scientists.
The UK has secured 30 million doses of the jab to roll out if approved by regulators, with the option of millions more.
Responding to the news about the successful trial of the Johnson & Johnson vaccine, Health Secretary Matt Hancock tweeted: "This is yet more good news from Janssen on vaccines.
"If this jab is approved this could significantly bolster our vaccination programme, especially as a single-dose vaccine.
"Once the full data has been submitted to the (Medicines & Healthcare products Regulatory Agency), they will consider the evidence to determine whether the vaccine meets robust standards of safety, effectiveness & quality.
"We're rolling-out vaccines as quickly as possible across the UK, with more than 7.4 million people given their first dose so far."
In the trial of nearly 44,000 volunteers, the level of protection against moderate and severe coronavirus was 66% in Latin America and just 57% in South Africa, where a particularly worrying variant of the coronavirus is circulating.
Those results compare to the high bar set by two authorized vaccines from Pfizer Inc/BioNTech SE and Moderna Inc, which were around 95% effective in preventing symptomatic illness in pivotal trials when given in two doses.
Those trials, however, were conducted mainly in the United States and before the broad spread of new variants now under the spotlight.
J&J's main study goal was the prevention of moderate to severe Covid-19, and the vaccine was 85% effective in stopping severe disease and preventing hospitalisation across all geographies and against multiple variants 28 days after immunisation.
That level of prevention "will potentially protect hundreds of millions of people from serious and fatal outcomes of Covid-19," Dr. Paul Stoffels, J&J's chief scientific officer, said in a statement.
The company plans to seek emergency use authorisation from the U.S. Food and Drug Administration next week.
Public health officials have been counting on the J&J vaccine to increase much-needed supply and simplify the U.S. immunisation campaign.
Unlike the Pfizer/BioNTech and Moderna vaccines, J&J's does not require a second shot weeks after the first or need to be kept frozen, making it a strong candidate for use in parts of the world with weak transportation infrastructure and insufficient cold storage facilities.
J&J has said it will produce the vaccine in the United States, Europe, South Africa and India.
