https://apnews.com/918bd56aa429e7755242b92f49dd7b41

Pfizer said Friday it was changing plans and testing three doses of its COVID-19 vaccine in babies and preschoolers instead of the usual two.

The addition of an extra dose came after a preliminary analysis found 2- to 4-year-olds didn't have as strong an immune response as expected to special low-dose shots.