• Johnson & Johnson said its Covid-19 booster shot is 94% effective when administered two months after the first dose.
• It also increases antibody levels by four to six times compared with one shot alone, J&J said.
• A J&J booster dose given six months out from the first shot appears to be potentially even more protective against Covid, the company said.

Johnson & Johnson said Tuesday its Covid-19 booster shot is 94% effective when administered two months after the first dose in the United States. It also said the booster increases antibody levels by four to six times compared with one shot alone.

A J&J booster dose given six months out from the first shot appears to be potentially even more protective against Covid, the company said, generating antibodies twelvefold higher four weeks after the boost, regardless of age.

When given as a booster, the vaccine remained well tolerated, with side effects generally consistent with those seen after the initial dose, according to J&J.

"We now have generated evidence that a booster shot further increases protection against COVID-19 and is expected to extend the duration of protection significantly," J&J chief scientific officer Dr. Paul Stoffels said in a statement.

The new data, provided in a press release, helps J&J make a case to the Food and Drug Administration to authorize a booster shot to some 14.8 million Americans who have received the company's single-dose vaccine.

The Biden administration announced plans last month to roll out booster shots for people who received the Moderna and Pfizer vaccines. An FDA advisory committee on Friday unanimously recommended Pfizer booster shots to people age 65 and older and other vulnerable Americans. A final decision from the agency is expected any day now.

U.S. health officials said they needed more data on the J&J vaccine before they can recommend boosters of those shots.

The 94% efficacy rate for the J&J booster shot is for the U.S., the company said. Globally, a booster shot given about two months after the first dose is 75% effective against symptomatic infection, according to the company. It also demonstrated 100% effectiveness against severe and critical disease, it said.

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

The new data on a single dose will help the "critical" need "to prioritize protecting as many people as possible against hospitalization and death given the continued spread of COVID-19 and rapidly emerging variants," the company said.

"A single-shot COVID-19 vaccine that is easy to use, distribute and administer that provides strong and long-lasting protection is crucial to vaccinating the global population," Stoffels said.