(CNN) -- In a much-anticipated announcement, Pfizer said Monday that a phase 2/3 trial showed its Covid-19 vaccine was safe and generated a "robust" antibody response in children ages 5 to 11.

These are the first such published results for this age group for a US COVID-19 vaccine, and the data has not yet been peer-reviewed or published. Pfizer said it plans to submit to the US Food and Drug Administration (FDA) for an emergency use authorization (EUA) soon.

The trial included 2,268 participants aged 5 to 11 years and used a regimen of two doses of the vaccine given 21 days apart. These trials used a 10-microgram dose, lower than the 30-microgram dose that has been used for those over 12 years of age.

"The 10-microgram dose was carefully selected as the preferred dose for safety, tolerability, and immunogenicity in children 5 to 11 years of age," Pfizer said in a news release.

The participants' immune responses were measured by looking at the levels of neutralizing antibodies in their blood and comparing those levels to a control group of people ages 16 to 25 who received a two-dose regimen with the largest dose of 30 micrograms. Pfizer said the levels compare well with those in older people who received the higher dose, showing a "strong immune response in this cohort of children one month after the second dose."

"In addition, the COVID-19 vaccine was well tolerated, with side effects generally comparable to those seen in participants aged 16 to 25 years," the company said.

A Pfizer spokesperson also confirmed that there were no cases of myocarditis, a type of heart inflammation that has been linked to mRNA vaccines.

Pfizer said this data will be included in a "short-term filing" for the US and that the companies will continue to amass the data needed to apply for FDA approval for people ages 5 to 11.

The Pfizer/BioNTech vaccine is currently approved for people 16 years of age and older, and licensed for use in people 12 to 15 years of age.

Pfizer said it expects trial data for children as young as 6 months "as soon as the fourth quarter of this year."

"Since July, pediatric cases of COVID-19 have increased by approximately 240% in the US, underscoring the need for public health vaccination. The results of these trials provide a strong basis for seeking authorization from our vaccine for children ages 5 to 11, and we plan to submit them to the FDA and other regulators urgently," Albert Bourla, Pfizer's chairman and CEO, said in the statement.

Acting FDA Commissioner Dr. Janet Woodcock and Dr. Peter Marks, director of the FDA's Center for Biological Evaluation and Research, said in a statement this month that the agency would review data on a vaccine for younger children. "as quickly as possible, probably in a matter of weeks rather than months," once it was submitted for clearance.

"However, the agency's ability to review these filings quickly will depend in part on the quality and timeliness of manufacturers' filings," they wrote.

Calls for a Covid-19 vaccine for younger children have grown louder in recent months as cases among children have risen.

Coronavirus infections have increased "exponentially" among children in the United States and now account for nearly 29% of all reported cases nationwide, the American Academy of Pediatrics reported last week.

Still, US health officials have stressed that children are not just little adults, and even those approaching 12 years old should not get the largest dose of vaccine available to the elderly.

"We don't want kids to have adverse effects. Of course, we want them to be able to get vaccinated as quickly as possible, but let's get it right," the FDA's Marks said at a fireside chat hosted by ResearchAmerica Alliance last week.

"There's a difference here because they're not just getting the same dose the same age as someone 12 or older. They have to get a reduced dose. And that's why it's not a good idea for doctors to take things at your own hands right now."