US drug company Pfizer said on Wednesday that its Covid-19 vaccine was 100 per cent effective in a final-stage trial in children aged 12 to 15.
This could pave the way in parts of the world for teenagers to be inoculated before the next school year.
The Pfizer-BioNTech vaccine is already authorised in many countries for people aged 16 and over.
Pfizer and its German partner BioNTech SE said they planned to submit the data to regulators in the US and Europe as soon as possible, seeking to amend their vaccine authorisations to include the younger age group.
In the study of 2,260 adolescents, the vaccine produced antibodies against Covid-19 that exceeded the level seen in vaccinated young adults, Pfizer and BioNTech said.
All 18 cases of Covid-19 in the study were in teenagers who received a placebo, the companies said. Side effects were consistent with those experienced by people between 16 and 25.
"We share the urgency to expand the authorisation 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," Pfizer chief executive Albert Bourla said.
The companies said they planned to submit more detailed results from the study to a scientific journal for publication.
In people 16 and older, the Pfizer-BioNTech vaccine was 95 per cent effective at preventing symptomatic cases in a final-stage trial, leading to its emergency authorisation late last year.
Last month, Pfizer and US drug company Moderna began trials of their vaccines in children under the age of 12. Moderna is also studying its vaccine in adolescents.
Both vaccines require people to get two doses.