Janssen’s single dose Covid-19 vaccine is 66% effective, the Belgian company has announced.

However, nobody needed hospital treatment or died from coronavirus after the vaccine took effect in the international trial.

Crucially, the trial looked at giving just one dose of the vaccine, which makes it significantly easier to roll out than those requiring two.

Although there are also signs the vaccine is less effective against the new variant that is spreading in South Africa.

The news comes shortly after Novavax announced their vaccine was 89% effective overall in the UK and 60% in South Africa. Both new vaccines will need to be reviewed by regulators before they can be used.

Janssen, a pharmaceutical company owned by Johnson & Johnson, is also investigating whether giving two doses will give either stronger or longer-lasting protection.

The fact the vaccine works as a single dose and can be kept in a standard fridge, while others need super-cold storage, means the vaccine could have a significant role around the world.

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Dr. Paul Stoffels, the chief scientific officer at Johnson & Johnson, said: “A one-shot vaccine is considered by the World Health Organization to be the best option in pandemic settings.”

He added the vaccine could “potentially protect hundreds of millions of people from serious and fatal outcomes of Covid-19”.

Janssen is aiming to make one billion doses in 2021.

The Janssen vaccine uses a common cold virus that has been engineered to make it harmless.

The vaccine then safely carries part of the coronavirus’s genetic code into the body. This is enough for the body to recognize the threat and then learn to fight coronavirus.

This trains the body’s immune system to fight coronavirus when it encounters the virus for real.

This is similar to the approach used by the University of Oxford and AstraZeneca.

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 hospitalizations and deaths would change the game in combating the pandemic.”

The results are based on nearly 44,000 people who took part in the trial and 468 cases of Covid-19.

However, the Janssen vaccine was just 57% effective in the South African part of the trial, where a new version of the coronavirus is spreading, compared with 72% in the US.