(WJW) – Johnson & Johnson announced Wednesday that using its COVID-19 vaccine as a booster shot increased antibodies nine-fold higher than the initial shot alone.

That’s according to clinical trial studies in people previously vaccinated with the single-shot vaccine, the company said in a press release.

According to J&J, the booster dose of the vaccine “generated a rapid and robust increase in spike-binding antibodies” 28 days after the primary single-dose shot in participants between the ages of 18 and 55 and in those 65 years and older.

“We have established that a single shot of our COVID-19 vaccine generates strong and robust immune responses that are durable and persistent through eight months,” said Mathai Mammen, M.D., Ph.D., Global Head, Janssen Research & Development, Johnson & Johnson. “With these new data, we also see that a booster dose of the Johnson & Johnson COVID-19 vaccine further increases antibody responses among study participants who had previously received our vaccine.”

Johnson & Johnson said it is working with the Food and Drug Administration, the Centers for Disease Control and Prevention and other health authorities regarding booster shots, and ongoing trials are underway.

“We look forward to discussing with public health officials a potential strategy for our Johnson & Johnson COVID-19 vaccine, boosting eight months or longer after the primary single-dose vaccination,” Mammen said.

Just over half of the U.S. population is fully vaccinated. Vaccinations in this country bottomed out in July at an average of about a half-million shots per day, down from a peak of 3.4 million a day in mid-April.

The delta variant has sent cases, deaths and hospitalizations soaring in recent weeks in the U.S., erasing months of progress. Deaths are running at about 1,000 a day on average for the first time since mid-March, and new cases are averaging 147,000 a day, a level last seen at the end of January.

Currently, the FDA has authorized third doses of either Pfizer’s or Moderna’s vaccine only for certain people with severely weakened immune systems, such as organ transplant recipients. For everyone else, the Biden administration is planning for boosters starting in the fall. But the FDA is evaluating that question separately.

This week, the FDA granted full approval to Pfizer’s vaccine, meaning it now carries its strongest endorsement of safety and effectiveness. Moderna has also applied for full approval, and Johnson & Johnson has said it hopes to apply later in the year. All three vaccines were initially given emergency use authorization.

The Associated Press contributed to this report.