Moderna's Covid-19 vaccine is safe and highly effective in children ages 12 to 17, the company said Tuesday.
It would be the second Covid-19 vaccine available for the age group if it is authorized for use, in addition to the Pfizer-BioNTech vaccine.
Two options would "increase the supply and choices of vaccines available to younger people," said Dr. Richard Besser, president of the Robert Wood Johnson Foundation, who is a former acting director of the Centers for Disease Control and Prevention.
The Moderna vaccine is given as two doses, four weeks apart. Moderna said its Phase 2/3 clinical trial included more than 3,700 participants, half of whom received the vaccine and half of whom received a placebo.
The company said there were four cases of Covid-19 among the placebo group starting two weeks after second doses were administered, compared with none in the vaccine group, meaning the vaccine was 100 percent effective.
When the company looked for milder cases of Covid-19 after just the first dose, the vaccine was shown to be 93 percent effective against any infection, not just symptomatic illness.
"We are encouraged" that the vaccine "was highly effective at preventing COVID-19 in adolescents," Moderna CEO Stéphane Bancel said in a statement. "It is particularly exciting to see that the Moderna COVID-19 vaccine can prevent SARS-CoV-2 infection."
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Side effects were generally mild or moderate, the company said, most commonly arm pain and, after the second dose, headache, fatigue, muscle aches and chills.
Moderna plans to submit the findings to the Food and Drug Administration in early June.
Moderna's vaccine was shown to be around 95 percent effective in clinical trials in preventing symptomatic illness in adults. Real-world data the CDC released in March found it to be about 90 percent effective.
The FDA lowered the age at which people can receive the Pfizer vaccine to 12 this month. Since then, more than 600,000 children ages 12 to 15 have had their first doses.
In March, Moderna started clinical trials of its vaccine in children ages 6 months to 11 years old.