Adolescents ages 12 to 15 were completely protected from symptomatic COVID-19 after being vaccinated with the Pfizer/BioNTech mRNA vaccine in a small Phase III clinical trial, Pfizer reported in a press release Wednesday.

The company also said that the vaccine was well-tolerated in the age group, spurring only the standard side effects seen in people ages 16 to 25. The vaccine is already authorized for use in people age 16 and over.

The vaccine appeared more effective at spurring defensive immune responses in adolescents ages 12 to 15 than in the 16- to 25-year-old group, producing even higher levels of antibodies that were able to neutralize SARS-CoV-2. In a measure of neutralizing antibodies, vaccinated youths in the new trial had geometric mean titers (GMTs) of 1,239.5, compared with the GMTs of 705.1 previously seen in those ages 16 to 25, Pfizer noted.

The trial involved 2,260 adolescents ages 12 to 15, of which 1,131 were vaccinated and 1,129 received a placebo. There were 18 cases of symptomatic COVID-19 in the trial, all of which were in the placebo group. In today’s press release, the company trumpeted that the vaccine demonstrated “100 percent efficacy.” The trial was not primarily designed to assess efficacy, however. It was primarily assessing relative immune responses, so it will require more data to fully evaluate efficacy. Additionally, Pfizer and BioNTech have only released top-line trial results, not the full data from the trial, which has not been peer-reviewed.

Last year, a Phase III trial involving more than 46,000 people found the vaccine to be 95 percent effective at preventing symptomatic COVID-19 in adults.

The hardy immune responses and demonstrated protection in the new adolescent trial are positive signs. Pfizer and BioNTech are now planning to submit the data to the US Food and Drug Administration, as well as regulators in the European Union, to expand use of the vaccine to adolescents.

“We share the urgency to expand the authorization of our vaccine to use in younger populations and are encouraged by the clinical trial data from adolescents between the ages of 12 and 15,” Albert Bourla, Pfizer’s CEO, said in the press release. “We plan to submit these data to FDA as a proposed amendment to our Emergency Use Authorization in the coming weeks and to other regulators around the world, with the hope of starting to vaccinate this age group before the start of the next school year.”

Last week, the companies announced the start of trials looking at safety and immune responses in infants and children ages 6 months to 11 years. The trial splits the children into three groups: ages 6 months to 2 years, 2 to 5 years, and 5 to 11 years. First doses went to children in the 5- to 11-year-old group last week, and the companies plan to start the 2- to 5-year group next week.

https://arstechnica.com/?p=1753451