Pfizer and BioNTech’s COVID-19 vaccine is 100% effective against the virus in children ages 12 to 15, the companies announced in a press release Wednesday.

In a placebo-controlled trial of 2,260 adolescents, none of the participants who received the real vaccine developed COVID-19, the companies said.

Eighteen adolescents who received placebo, or fake, doses became infected with the virus, they said.

The COVID-19 vaccine was “well-tolerated” by the age group, the companies said, with participants experiencing a similar range of side effects as seen in older teens and young adults.

Experts say that ensuring vaccines are safe and effective in children will be crucial to ending the pandemic. Although children are less likely to die of COVID-19, it’s still possible for them to get sick and spread the virus.

Pfizer CEO Albert Bourla said in a statement that he was “encouraged” by the clinical trial data, and that the company plans to submit the data to the U.S. Food and Drug Administration “in the coming weeks” to update its emergency use authorization to include children 12 and older.

The company hopes to start vaccinating children ages 12 to 15 “before the start of the next school year,” Bourla said.

Experts say it’s important to test vaccines in children to ensure they are safe and effective in the youngest members of society so that ultimately everyone is eligible to receive a potentially lifesaving vaccine.

Last week, Pfizer and BioNTech launched a global COVID-19 vaccine trial that will ultimately enroll 4,500 children between the ages of 6 months and 11 years old.

Their vaccine is currently authorized to be distributed in the U.S. for use in people ages 16 and up.

Other vaccine manufacturers have been moving to offer their vaccines to children. Moderna announced earlier this month that it would enroll 6,750 children ages 6 months to 12 years old in a clinical trial.

Johnson & Johnson also has said it intends to develop trials for children. Moderna and Johnson & Johnson’s vaccines have been granted emergency use authorization by the FDA for those ages 18 and older.

ABC News’ Eric Strauss contributed to this report.