NEW YORK — Johnson & Johnson said on Tuesday that its one-shot COVID-19 vaccine has performed well in real-world studies, offers long-lasting protection against the virus and boosts the immune system when administered as a booster a few months after the original dose.

The company made the announcement in a release of late-stage clinical data for the adenovirus-based vaccine, produced by Johnson & Johnson subsidiary Janssen, which was given emergency use authorization in the United States early this year.

Johnson & Johnson said it performed two studies in which volunteers received a second vaccine dose between two and six months after the first. It said the booster led to an increased immune response in recipients between 18 and 55 years old.

When given two months after the first dose, the company said the booster shot was 100% effective in protecting recipients from severe COVID-19 and was 75% effective in preventing symptomatic COVID-19 worldwide. It was 94% effective in preventing symptomatic COVID-19 in the United States, the data said.

“When a booster of the Johnson & Johnson COVID-19 vaccine was given two months after the first shot, antibody levels rose to four to six times higher than observed after the single shot,” the company said.