A two-dose version of Johnson & Johnson’s coronavirus vaccine provides 94% protection against symptomatic infection, the company said Tuesday — making a two-dose regimen of the Johnson & Johnson Janssen vaccine comparable to a two-dose regimen of Moderna’s or Pfizer’s.

Plus, the company said, adding a booster dose to a single shot of the vaccine raised immunity even more, and should also protect people strongly against infection.

The company released some details of three studies looking at various aspects of its Janssen vaccine, and said that, taken together, they showed the vaccine provided long-lasting protection that could be boosted with an extra shot.

Johnson & Johnson’s single-dose vaccine was given emergency use authorization by the US Food and Drug Administration on February 27. It has been given to about 14.8 million Americans, according to the US Centers for Disease Control and Prevention.

The company’s ongoing Phase 2 trial of a two-dose regimen showed giving two doses 56 days apart provided 100% protection against severe COVID-19 and 94% protection against moderate to severe COVID-19 in the United States. Globally, the two-dose regimen provided 75% protection against moderate-to-severe COVID-19, the company said.

A second study showed people given a booster shot six months or longer after their first dose had a 12-fold increase in antibodies — compared to a four-fold increase for people who got a second dose at two months.