The Johnson & Johnson covid-19 vaccine only needs one dose. It’s the third covid-19 vaccine to get sign-off from the agency.

The vaccine can be administered to people 18 years and older. In the United States, it was 72 percent effective against severe and milder covid-19. In South Africa, a variant form of the coronavirus is widespread.

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The Johnson & Johnson vaccine is logistically easier to distribute than the Moderna and Pfizer / biontech vaccines, which take two doses and have to be stored in specialized freezers.

The Johnson & Johnson vaccine was built using a different technology than the Moderna and Pfizer / biontech vaccines. Those two are gene-based vaccines, a strategy that delivers the genetic material for a bit of the coronavirus into the body.

The Moderna and Pfizer / biontech vaccines were tested in the US and other countries before variants appeared. Clinical trials found that they were around 95 percent protective against symptomatic covid-19.

The Johnson & Johnson vaccine was just as good as the other two at protecting people from being hospitalized or dying from covid-19.

‘Johnson & Johnson appears to be just as good as Moderna and Pfizer at preventing those,’ said Ashish Jha, Dean of the Brown University School of public health.

Johnson & Johnson has around 4 million doses ready to ship in the US. The company originally said it could have 12 million ready by the end of February. Manufacturing delays undercut that plan.