Pfizer tests extra shot for kids under 5 in setback

Pfizer said Friday it was changing plans and testing three doses of its COVID-19 vaccine in babies and preschoolers after the usual two shots didn’t appear strong enough for some of the children.

Pfizer announced the change after a preliminary analysis found 2- to 4-yearolds didn’t have as strong an immune response as expected to the very low-dose shots the company is testing in the youngest children.

It’s disappointing news for families anxious to vaccinate their tots. Pfizer had expected data on how well the vaccines were working in children under 5 by year’s end, and it’s not clear how long the change will delay a final answer.

Pfizer and its partner Biontech said if the threedose 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 5- to 11-yearolds, 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.

The very low-dose shots appeared to work in youngsters under age 2, who produced similar antibody levels. But the immune response in 2- to 4-year-olds was lower than the study required, Pfizer vaccine research chief Kathrin Jansen said Friday in a call with investors.

Rather than trying a higher-dose shot for the preschoolers, Pfizer decided to expand the study to evaluate three of the very low-dose shots in all the study participants — from 6 months up to age 5. That third shot will come at least two months after the youngsters’ second dose.