WASHINGTON, April 9 (Reuters) - Pfizer and its German partner BioNTech said on Friday (Apr 9) they have requested the US Food and Drug Administration to expand the emergency use of their COVID-19 vaccine in adolescents aged 12 to 15.

In late March they published the results of trials carried out with 2,260 adolescents in the US who the companies said showed "robust anti-body responses".

The vaccine was "well tolerated with side effects generally consistent with those observed in participants 16 to 25 years of age," the companies said on Friday.

Whether COVID-19 vaccines work and are safe to use on children is one of the big questions drugmakers are trying to answer. Inoculating children and young people is considered a critical step toward reaching "herd immunity" and taming the pandemic, according to experts.

The companies plan to request similar rulings by other regulatory authorities globally in the coming days.

The Pfizer-BioNTech two-shot vaccine is already authorised for use in people as young as 16.