The Janssen developed Covid vaccine is 66 per cent effective and can be fully administered through just one dose, the Belgian company has announced.
The UK has already pre-ordered 30 million doses of the vaccine.
The announcement comes after Novavax revealed its Covid-19 jab was 89 per cent effective from one dose.
A vaccine’s efficacy is estimated by comparing the numbers of new cases in vaccinated and unvaccinated people. This is normally done through a randomised control trial, which sees volunteers receive an injection. At random, volunteers receive either the actual vaccine or a placebo jab, not knowing which they are getting.
A 66 per cent efficacy means a 66 per cent reduction in new cases of the disease in the vaccine group, compared with the placebo group.
Both vaccines will need to be reviewed by regulators before they can be distributed for immunisations.
‘Potentially protect hundreds of millions of people’
The Janssen vaccine is produced by using a common cold virus that has been engineered to make it harmless.
Similar to the Oxford/AstraZeneca jab, the vaccine then safely carries part of the coronavirus’s genetic code to the body. The body learns to recognise the threat and then learns to fight the coronavirus.
This then trains the body’s immune system to fight off coronavirus if it encounters the true virus.
The chief scientific officer at Johnson & Johnson, Dr Paul Stoffels, said the vaccine would “potentially protect hundreds of millions of people from serious and fatal outcomes of Covid-19”.
Dr Mathai Mammen, from Janssen, said: "A single-dose regimen with fast onset of protection and ease of delivery and storage provides a potential solution to reaching as many people as possible.
The ability to avoid hospitalisations and deaths would change the game in combating the pandemic."
However, the efficacy rate reported by Janssen is lower than that of the jabs already authorised from BioNTech/Pfizer, Modern and Oxford/AstraZeneca.The efficacy rate can not be directly compared with other vaccines because the trial did not include mild cases of the disease.
The Janssen vaccine reported an efficacy rate of just 57 per cent in the South African part of the trail, where a new variant of the coronavirus is spreading.