Pfizer stated Friday that they were changing their plans and will now test three doses (preschoolers and babies) of COVID-19 vaccine.

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 was planning to publish data from the study on children younger than 5 years by the close of the year. It’s not clear how this change will delay the quest to vaccinate the youngest children.

Pfizer said that BioNTech, its partner in Pfizer’s three-dose trial is a success and they will apply for an emergency authorization within the first half 2022.

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.

Pfizer has tested a smaller dose for children under 5 years old, which is just 3 micrograms. This dose represents a tenth the adult dose.

A subset was selected from the group of children in the study and tested for virus-fighting antibody levels a month later.

Kathrin Jansen from Pfizer, chief of vaccine research, said that younger children under 2 have similar levels of antibody, while their immune response was lower in 2- and 4-year-olds, in an interview with investors.

This study has been expanded to include the evaluation of three very low dose shots given to children younger than 5. That third shot will come at least two months after the youngsters’ second dose.

The companies stated that no safety concern was found in the study.

Jansen also cited data that showed that a booster shot given to people aged 16 or older increases protection. Scientists hope this will prevent the new Omicron variant.

Companies are also preparing to test boosters for children aged 5-11 years old, who have just received their second-dose vaccines. They are also testing different dosage options for boosters for teens.

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


The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. All content is the sole responsibility of the Associated Press.


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