(AP)- Pfizer is testing an extra dose of its COVID-19 vaccine for babies and preschoolers enrolled in a study of the shots. Pfizer had been testing two very low-dose shots in children under age 5, with some data expected by year’s end. But Pfizer and its partner BioNTech announced Friday they were adding a third dose to the study after a preliminary analysis found 2- to 4-year-olds didn’t have as strong an immune response as expected. It’s not clear how much the study change will delay the quest for vaccinating the youngest children.
Photo: A boy receives a dose of Pfizer-BioNTech COVID-19 vaccination for children aged 5 – 11, in Rome, Wednesday, Dec. 15, 2021. (AP Photo/Andrew Medichini)