Two doses of the Pfizer-BioNTech Covid-19 vaccine offer almost no protection against coronavirus infection in kids ages 5 to 11, according to new data posted online — a finding that may have consequences for parents and their vaccinated children.
Researchers from the New York State Department of Health found that the vaccine’s effectiveness dropped to 12 percent from 68 percent in the age group in December and January, when the omicron variant of the coronavirus began circulating widely in the United States.
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The Pfizer shots still offered protection against serious illness from Covid, the researchers found, with protection against hospitalization declining to 48 percent from 100 percent over the same time period.
The findings, which were posted to a preprint server Monday and have not yet been peer-reviewed, looked at the health records for Covid cases in children and teens in New York between Dec. 13 and Jan. 30.
It may be a setback for parents with vaccinated children who were hoping to resume “normal” pre-pandemic activities. The Pfizer-BioNTech vaccine is the only Covid shot in the U.S. available to kids in this age group.
More than 7 million children ages 5 to 11 — about 25 percent — have received two doses of a Covid vaccine, according to data from the Centers for Disease Control and Prevention.
The large drop in the vaccine's effectiveness against infection may be due in part to the smaller vaccine dosage given to kids 5 to 11, said Dr. Peter Hotez, co-director of the Center for Vaccine Development at Texas Children’s Hospital. He helped develop another Covid shot that uses old vaccine technology.
The Food and Drug Administration authorized a vaccine dosage of 10 micrograms for kids ages 5 to 11, one-third the dosage given to everyone 12 and up. The two doses are given three weeks apart.
The New York state researchers, who also examined vaccine data in children ages 12 to 17, found the shots performed better in older children, who are given a higher dosage.
Vaccine effectiveness against infection in older kids fell to 51 percent from 66 percent, according to the data. Vaccine effectiveness against hospitalization dropped to 73 percent from 85 percent.
"It’s looking more likely that at the current lower dose of the Pfizer-BioNTech vaccine for the 5- to 11-year-olds, a third dose may be required," Hotez said.
It’s unclear if Pfizer will seek FDA authorization of a booster dose for kids 5 to 11. The company told NBC News in a statement that it is confident in the protection and safety of its Covid vaccine, though early data suggests people vaccinated with three doses may have a higher degree of protection.
Dr. Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, said it will be hard to determine whether a higher dosage or another shot is needed in kids 5 to 11 because the omicron variant has also already been shown to evade some of the immunity in vaccinated or boosted adults.
“I don’t think you can tell yet because omicron is immune evasive, so therefore even if you’re vaccinated, you’re not going to be as well protected,” he said.
For now, it is reassuring that the vaccine appears to hold up some against serious illness, Offit said, though some children may be susceptible to mild illness.
Hotez said while the vaccine is holding up against severe illness, it is unclear whether that level of protection is continuing to diminish or if it is simply because of the omicron variant.
About two weeks ago, Pfizer said it was postponing its vaccine application to the FDA for children ages 6 months to 4 years after it found two doses didn’t work well in children ages 2 to 4.
The company said it will wait for its data on a three-dose series of the vaccine.
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