Johnson & Johnson announced Tuesday that its Covid-19 booster is 94% effective when given two months after the first dose in the United States. The booster is also said to increase antibody levels four to six times compared to an injection alone.

A J&J booster dose given six months after the first injection appears to have potentially even better protection against Covid, the company said, and generates twelve times higher antibodies four weeks after the booster, regardless of age.

When used as a booster, the vaccine was well tolerated, with side effects generally similar to those seen after the initial dose, according to J&J.

“We have now provided evidence that a booster vaccination will further increase protection against COVID-19 and is likely to extend the duration of protection significantly,” said Dr. Paul Stoffels, J & J’s Chief Scientific Officer, in a statement.

The new data, provided in a press release, will help J&J file a case with the Food and Drug Administration to approve a booster vaccination for approximately 14.8 million Americans who received the company’s single-dose vaccine.

The Biden government last month announced plans to introduce booster vaccinations for people who have received the Moderna and Pfizer vaccines. An FDA advisory committee on Friday unanimously recommended Pfizer booster vaccinations for people 65 years and older and other at-risk Americans. A final decision from the agency is now expected every day.

US health officials said they need more data on the J&J vaccine before they can recommend boosters of those vaccinations.

The 94% effectiveness rate for the J&J booster is in the United States, the company said. According to the company, a booster shot about two months after the first dose is 75% effective against symptomatic infections worldwide. It also showed 100% effectiveness against serious and critical illnesses, it said.

The company also released data from a real-world study that found that a single dose of its vaccine provided strong and long-lasting protection against hospital stays related to Covid, and showed 81% effectiveness after several months.

The new single-dose data will help ensure that “protecting as many people as possible from hospitalizations and deaths is a priority given the continued spread of COVID-19 and rapidly emerging varieties,” the company said.

“A unique COVID-19 vaccine that is easy to use, distribute and administer, that offers strong and long-lasting protection, is critical to vaccinating the world’s population,” Stoffels said.