Moderna’s COVID-19 vaccine appears safe and highly effective in adolescents ages 12 to 17, according to the top-line results of a small clinical trial the company announced Tuesday.

The company plans to submit the trial data to the US Food and Drug Administration early next month, seeking authorization for expanded use in the age group.

If the FDA grants the authorization, Moderna’s vaccine will be the second COVID-19 vaccine available for use in kids as young as 12 in the US. Earlier this month, the FDA authorized the Pfizer-BioNTech vaccine for use in adolescents ages 12 to 15. (The Pfizer-BioNTech vaccine was initially authorized for use in people ages 16 and up, while Moderna’s was initially authorized for use in people ages 18 and up.)

For the clinical trial, researchers enrolled 3,732 adolescents ages 12 to 17. Two-thirds were randomly assigned to get the vaccine, while the remaining third received a placebo. The vaccinated group produced immune responses as strong as those seen in vaccinated adults, Moderna reported in a press release Tuesday.

There were no cases of symptomatic COVID-19 among adolescents who had received both doses of the Moderna vaccine; there were four cases in the placebo group. The company noted that this was “consistent with a vaccine efficacy of 100 percent.” However, the trial was primarily designed to evaluate immune responses in adolescents, not to establish efficacy rate.

Researchers also looked for very mild infections after trial participants received their first shot. Mild infections were defined as those in adolescents with a positive coronavirus test but just one COVID symptom (rather than two or more, which is often used). Using this definition, researchers found that just one shot of the vaccine was 93 percent effective.

The vaccine appeared safe in the young group and produced no serious side effects. Adolescents reported similar mild to moderate side effects as adults, including pain at the injection site after the first shot and headache, fatigue, myalgia, and chills after the second.

In a statement, Moderna CEO Stéphane Bancel said the company was “encouraged” by the results. “We will submit these results to the U.S. FDA and regulators globally in early June and request authorization. We remain committed to doing our part to help end the COVID-19 pandemic.”