Pfizer expands vaccine tests in kids under 12

says it is expanding testing of its COVID-19 vaccine in children younger than 12.

After a first-step study in a small number of young children to test different doses, Pfizer is ready to enroll about 4,500 young volunteers at more than 90 sites in the U.S., Finland, Poland and Spain.

The vaccine made by Pfizer and its German partner BioNTech already is authorized for emergency use in anyone 12 and older in the U.S. and European Union.

Enrollment of 5- to 11-year-olds began this week. Those youngsters will receive two vaccine doses of 10 micrograms each -- a third of the teen and adult dose -- or dummy shots. Enrollment of children as young as 6 months will start in a few weeks using an even lower dose, 3 micrograms per shot.