The Food and Drug Administration’s scientists confirmed that overall the vaccine is about 66% effective at preventing moderate to severe COVID-19. The agency also said J&J’s shot — one that could help speed vaccinations by requiring just one dose instead of two — is safe to use.

That’s just one step in the FDA’s evaluation of a third vaccine option for the U.S. On Friday, the agency’s independent advisers will debate if the evidence is strong enough to recommend the long-anticipated shot. Armed with that advice, FDA is expected to make a final decision within days. ...

&J tested its single-dose option in 44,000 people in the U.S., Latin America and South Africa. Different mutated versions of the virus are circulating in different countries, and the FDA analysis cautioned that it’s not clear how well the vaccine works against each variant. But J&J previously announced the vaccine worked better in the U.S. -- 72% effective against moderate to severe COVID-19, compared with 66% in Latin America and 57% in South Africa.

Still, in every country it was highly effective against the most serious symptoms, and early study results showed no hospitalizations or deaths starting 28 days after vaccination. ...