Pfizer says it will expand testing of its COVID-19 vaccine to children younger than 12.  The drug company, along with its German partner BioNTech, will enroll 4,500 children volunteers at more than 90 places in the U.S., Finland, Poland and Spain.  The children, ages 5 to 11, will be given two doses of 10 micrograms each, which is about a third of the dose used on teens and adults. Some will receive placebo shots.  Testing on infants as young as 6 months will start within weeks. They will receive 3-microgram doses. The Pfizer-BioNTech vaccine already has been given authorization for emergency use for those 12 and older in the U.S. and Europe. 
 
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