Pfizer-BioNTech vaccine doses of 30 micrograms are used for children over 12 in the EU, US, and Canada.

The study will enroll some 4,500 children at 90 clinical sites in the United States, Finland, Poland, and Spain, the company said. Pfizer said it will use a dose of 10 micrograms for children between 5 and 11 and 3 micrograms for children under 5.

The company said in March that its vaccine is 100% effective in children ages 12-15.

According to US media, inoculating children more than 6 months old is considered a critical step toward reaching herd immunity and taming the COVID-19 pandemic.