In December, Pfizer announced that it decided to add a third dose to the primary vaccine regimen for young children. It said the original two-dose series did not provide the expected immunity in 2- to 5-year-olds.
In December, Pfizer announced that it decided to add a third dose to the primary vaccine regimen for young children. It said the original two-dose series did not provide the expected immunity in 2- to 5-year-olds.