The Johnson & Johnson Covid-19 vaccine is licensed in the US, only one shot and is cost effective

 The Johnson & Johnson vaccine is the third approved vaccine in the US.

However the other vaccine is a two-dose vaccine.

The company agreed to provide 100 million doses to the US by the end of June. The first dose could be made available to the US population as early as next week.

The UK, EU and Canada have also ordered, and 500 million doses have also been ordered through the Covax scheme to be distributed to poor countries.

President Joe Biden called the news "good news for all Americans, and an exciting development," but warned that "the fighting is not over".

Even though we celebrate today's news, I ask all Americans - continue to wash their hands, keep their distance and wear masks, "he said in a press statement.

"As I often say, the situation is still likely to get worse as new variants spread, and current developments may reverse."

The authorization from the US Food and Drug Administration (FDA) comes after an external committee of experts unanimously endorsed the vaccine on Friday.

Results from trials conducted in the US, South Africa, and Brazil showed the Johnson & Johnson vaccine was more than 85% effective in preventing serious illness, and was generally 66% effective when symptomatic cases were taken into account.

Notably, there were no deaths among participants who received the vaccine and none of the participants admitted to hospital 28 days post-vaccine.

Overall protection is lower in South Africa and Brazil, where variants of the virus have become dominant, but protection against serious or critical illness is "equally high."

South Africa started giving health workers an unapproved Johnson & Johnson vaccine as part of the study earlier this month. This comes after preliminary research shows that the Oxford-AstraZeneca vaccine provides "minimal protection" against mild symptomatic disease caused by the dominant variant in most of the country.

So far the only other country that has approved a Johnson & Johnson vaccine for emergency use is Bahrain, which gave the green light on Thursday.

Because this vaccine requires less doses than the dual-dose Pfizer and Moderna vaccines, it also requires fewer appointments and medical staff.