Vaccine maker Pfizer said Friday that trials of its vaccine in children ages 2 to 5 show that it did not provide the expected immunity in kids this age, and it is adding a third dose to the regimen.
Vaccine maker Pfizer said Friday that trials of its vaccine in children ages 2 to 5 show that it did not provide the expected immunity in kids this age, and it is adding a third dose to the regimen.