Moderna said Monday that a low dose of its COVID-19 vaccine is safe and appears to work in 6- to 11-year-olds, as the manufacturer moves toward expanding shots to children.

Competitor Pfizer's kid-sized vaccine doses are closer to widespread use, undergoing evaluation by the Food and Drug Administration for nearly the same age group - starting at age 5. Its vaccine already is authorized for anyone 12 or older.

Moderna hasn't yet gotten the nod to offer its vaccine to teens but is studying lower doses in younger children while it waits. Researchers tested two shots for the 6- to 11-year-olds, given a month apart, that each contained half the dose given to adults.

Preliminary results showed vaccinated kids developed virus-fighting antibodies similar to levels that young adults produce after full-strength shots, Moderna said in a press release.

The study included 4,753 kids ages 6 to 11, who got either the vaccine or dummy shots. Moderna said that like adults, the vaccinated youngsters had temporary side effects including fatigue, headache, fever and injection site pain.

The study was too small to spot any extremely rare side effects, such as heart inflammation that sometimes occurs after either the Moderna or Pfizer vaccines, mostly among young men.

Moderna said it plans to submit its pediatric data to the FDA and global regulators soon. The FDA hasn't yet ruled on the company's application to expand its vaccinations to 12- to 17-year-olds, although some countries have cleared Moderna's shots for adolescents.

But the U.S. is expected to begin vaccinating kids under 12 sometime next month, if the FDA clears small doses of the Pfizer and BioNTech vaccine for 5- to 11-year-olds. Pfizer reported last week that its kid-sized doses proved nearly 91% effective at preventing symptomatic COVID-19 in the younger age group, even as the extra-contagious delta variant was spreading widely.

FDA's advisers will deliberate Pfizer's evidence in a public meeting Tuesday. If the agency authorizes Pfizer's kid shots, the Centers for Disease Control and Prevention the following week is set to recommend who should receive them.