Pfizer's COVID-19 vaccine was highly effective in a trial of 12- to 15-year-olds, paving the way for adolescents to get it in the US and Europe

• Pfizer-BioNTech's COVID-19 vaccine was highly effective in a trial in more than 2,000 adolescents.
• Pfizer said the vaccine was "well tolerated" in teens ages 12 to 15.
• Pfizer's CEO said Wednesday that he hoped to get kids vaccines by September.

The Pfizer-BioNTech coronavirus vaccine was highly effective at preventing COVID-19 infection in a late-stage trial in kids ages 12 to 15, the companies announced Wednesday.

The companies said that the vaccine generated a strong immune response in adolescents and that none of the kids who received the vaccine got sick with COVID-19. The results were published in a press release, and the companies said they planned to submit them to a scientific publication for review and to regulators for authorization within weeks.

The two-dose Pfizer-BioNTech vaccine is authorized in 66 countries for those over 16 years old, including the US. While younger people typically don't develop the most severe cases of COVID-19, getting children vaccinated could help reach herd immunity and reopen schools.

Pfizer CEO Albert Bourla said he hoped the results would allow countries to start vaccinating adolescents "before the start of the next school year."

Pfizer tested the vaccine in about 2,000 adolescents

The companies tested the vaccine about 2,000 peoples ages 12 to 15. Half of them received two doses of the vaccine and half received two placebo injections.

None of the kids who got the vaccine came down with COVID-19, while 18 cases were reported in the group that got a placebo shot. The companies touted this result as 100% efficacy.

Pfizer said side effects were similar for 12- to 15-year-olds as for those ages 16 to 25 but did not detail what they were. Generally, side effects of Pfizer's vaccine last for a couple of days and include fevers, headache, tiredness, and pain, redness, or swelling around the injection site.

So far, more than 26.7 million adult Americans have been fully immunized with two doses of Pfizer's vaccine, according to the Centers for Disease Control and Prevention.

Pfizer plans to submit the data to the US Food and Drug Administration and the European Medicines Agency to request emergency authorization of the vaccine for use in adolescents.

Pfizer and BioNTech are also testing the vaccine in younger people. The companies started trials in 5- to 12-year-olds on Sunday and said Wednesday that they planned to initiate trials in children ages 2 to 5 next week.

Read more: COVID-19 Vaccine Tracker: AstraZeneca's shot proves safe and effective and is headed to the FDA

Drug companies want to make COVID-19 shots available to younger people

COVID-19 vaccines from Moderna, AstraZeneca-Oxford University, and Johnson & Johnson are authorized for people over 18 only. Those companies are also working to make them available to younger people.

Moderna announced March 16 that it had started testing its COVID-19 vaccine in kids ages 6 months to 12 years in the US and Canada.

AstraZeneca is testing its vaccine in kids ages 6 to 17, the company announced February 15.

Johnson & Johnson's CEO, Alex Gorsky, said March 3 that the company was likely to have a COVID-19 vaccine available for children under 18 by September, per The Washington Post.

Dr. Scott Gottlieb, the former head of the US Food and Drug Administration, told CNBC on Wednesday, that the infection rates in under-16s in Israel - where more than half of the population is fully immunized with Pfizer's shot - "dropped dramatically" once adults got vaccinated as infection rates fell. Gottlieb is also a member of Pfizer's board of directors.

"The best way to protect children is to get adults vaccinated," he said.