Johnson & Johnson on Tuesday asked the Food and Drug Adminstration to authorize a booster dose of its Covid-19 vaccine for people 18 and older.

The company did not specify how long after initial vaccination the second, booster dose should be given. J&J submitted data to the FDA in September it said showed that a booster shot given two to six months after an initial dose bolstered antibody protection against Covid.

J&J said Monday that giving a second dose two months after the first increased protection against symptomatic moderate to severe Covid-19 to 94 percent, with 100 percent protection against severe illness.

"A booster of our COVID-19 vaccine increases levels of protection for those who have received our single-shot vaccine to 94 percent," said Mathai Mammen, global head of research and development at J&J's Janssen subsidiary. “At the same time, we continue to recognize that a single-shot COVID-19 vaccine that provides strong and long-lasting protection remains a crucial component to vaccinating the global population.”

The Food and Drug Administration's independent vaccine advisory committee is scheduled to meet on Oct. 15 to consider the J&J booster shot, clearing the way for the agency to make a final decision about whether to authorize its use.

The timing of the meeting is unusual: FDA does not normally announce an advisory panel will gather to discuss an application before one is filed. But the Biden administration is pushing to roll out Covid-19 boosters quickly this fall to prevent a fall or winter surge as temperatures grow colder and people head indoors, including for the holiday season.

The agency has authorized a booster shot from Pfizer and BioNTech for the elderly and for younger adults with jobs or underlying health conditions that increase their risk of severe Covid-19.

Background: J&J's single-dose vaccine has had limited uptake domestically since the federal government paused its use in April over concerns about blood clotting post-inoculation. The company's U.S. production was also interrupted for months by problems at a contractor's plant.

The initial efficacy of the two other vaccines authorized or approved for use in the U.S., Pfizer's and Moderna's messenger RNA products, also has outshone that of Johnson & Johnson's. J&J said earlier this year that a single shot of its vaccine provided 66 percent protection against moderate and severe disease; the mRNA vaccines posted effectiveness rates above 90 percent.

Still, J&J's shot has held up against the highly contagious Delta variant, with the company promoting a small lab study last summer finding robust levels of neutralizing antibodies against the strain in vaccine recipients.

So far, roughly 15 million people have gotten the J&J vaccine, compared to nearly 103 million for Pfizer and about 68 million for Moderna, according to CDC data.

What's next: FDA will consider the booster application over the coming weeks. The next major development will come at the Oct. 15 advisory committee meeting.