Pfizer study tests extra COVID vaccine dose for kids under 5

Brianna Ocampo, 8, receives her second dose of the Pfizer COVID-19 vaccine from Lurie Children's hospital registered nurse Yorman Gomez at Northwest Community Church in Chicago, Saturday, Dec. 11, 2021. Ann & Robert H. Lurie Children's Hospital's mobile vaccine clinic visited Belmont Cragin to help ensure adults and kids can be fully-vaccinated for the holiday season. 
The clinic was not be providing Dose 1 of the vaccine, and only provided youth and adult Dose 2, Dose 3 and booster vaccines. (AP Photo/Nam Y. Huh)

Brianna Ocampo, 8, receives her second dose of the Pfizer COVID-19 vaccine from Lurie Children's hospital registered nurse Yorman Gomez at Northwest Community Church in Chicago, Saturday, Dec. 11, 2021. Ann & Robert H. Lurie Children's Hospital's mobile vaccine clinic visited Belmont Cragin to help ensure adults and kids can be fully-vaccinated for the holiday season. The clinic was not be providing Dose 1 of the vaccine, and only provided youth and adult Dose 2, Dose 3 and booster vaccines. (AP Photo/Nam Y. Huh)

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.

Pfizer had planned to release data from its study of children under 5 by the end of the year. It’s not clear how this change will delay the quest to vaccinate the youngest children.

Pfizer and its partner BioNTech said if the three-dose study is successful, they plan to apply for emergency authorization sometime in the first half of 2022.

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A kid-sized version of Pfizer’s vaccine already is available for 5- to 11-year-olds, one that’s a third of the dose given to everyone else 12 and older.

For children younger than 5, Pfizer is testing an even smaller dose, just 3 micrograms or a tenth of the adult dose.

Researchers analyzed a subset of youngsters in the study a month after their second dose to see if the tots developed levels of virus-fighting antibodies that were similar to teens and young adults who get the regular shots.

Youngsters under age 2 had similar antibody levels, but the immune response in 2- to 4-year-olds was lower, Pfizer vaccine research chief Kathrin Jansen said Friday in a call with investors.

So the study is being expanded to evaluate three of those very low-dose shots in children under 5. That third shot will come at least two months after the youngsters’ second dose.

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No safety concerns have been spotted in the study, the companies said.

Jansen cited other data showing a booster shot for people 16 and older restores strong protection, a jump in immunity that scientists hope also will help fend off the new omicron variant.

The companies also are preparing to test a booster for 5- to 11-year-olds, who are just now getting their two-dose vaccinations. And they are testing different dose options for teen boosters.

Jansen said if the additional pediatric testing is successful, “we would have a consistent three-dose vaccine approach for all ages.”

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

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