Health and Science

Pfizer study tests extra Covid vaccine dose for kids under 5

Key Points
  • With just two doses, children under age two developed a sufficient immune response to Covid, but those between two- and four-years-old did not.
  • It's still not clear when children younger than five will have access to a Covid-19 vaccine.
  • Pfizer is testing a small size vaccine dose in kids under five, just one tenth of an adult dose.

In this article

Pfizer/BioNTech's pediatric COVID-19 vaccine vials are seen in this undated handout photo.
Pfizer | Reuters

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 two- to four-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 five 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.

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

For children younger than five, Pfizer is testing an even smaller dose, just three 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 two had similar antibody levels, but the immune response in two- to four-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 five. That third shot will come at least two months after the youngsters’ second dose.

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 five- 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.”