CNN  — 

A third shot of the children’s dose of Pfizer/BioNTech’s Covid-19 vaccine raised Omicron-fighting antibodies by 36 times in kids 5 through 11 years of age, the companies said in a news release Thursday. The companies plan to request emergency use authorization from the US Food and Drug Administration for a booster dose for this age group.

The new data come from a small study of 140 children ages 5 through 11 who were given a third 10-microgram dose of the Pfizer-BioNTech Covid-19 vaccine at least six months after their second dose.

The researchers analyzed antibody levels in serum – the clear part of the blood – from a subset of 30 children in this group one month after their third shot and found that antibodies against the Omicron variant were 36 times higher than they had been after the second dose of the vaccine.

In an analysis from 140 children with no evidence of prior Covid-19 infection, antibody levels against the original strain of the SARS-CoV-2 virus were six times higher one month after a booster dose than a month after the second vaccine dose.

The companies said there were no safety issues associated with a booster dose of the vaccine in these small groups of children.

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Pfizer and BioNTech say they will ask the FDA for an emergency use authorization, or EUA, for a booster dose for children in this age group “in the coming days.” They will also share the data with the European Medicines Agency and other regulatory agencies.

Studies from the New York State Department of Health and the US Centers for Disease Control and Prevention found that the effectiveness of Pfizer’s vaccine for children ages 5-12 dropped substantially during the Omicron surge, falling from 68% to about 12% against Covid-19 infection. However, two doses of the vaccine continued to provide protection against more severe illness resulting in urgent care or hospitalizations.

The primary series of two doses was authorized by the FDA for emergency use in this age group in October.

Booster doses of Pfizer’s Covid-19 vaccine are already authorized for people age 12 and older.