The coronavirus vaccine made by Pfizer-BioNTech is much less effective in preventing infection in children ages 5 to 11 years than in older adolescents or adults, according to a large new set of data collected by health officials in New York State — a finding that has significant ramifications for these children and their parents.
The Pfizer vaccine is the only Covid-19 shot authorized for that age group in the United States. It still prevents severe illness in the children, but offers virtually no protection against infection, even within a month after full immunization, according to the data, which were collected during the Omicron surge.
The sharp drop in the vaccine’s performance in young children may stem from the fact that they receive one-third the dose given to older children and adults, researchers and federal officials who have reviewed the data said.
The findings, which were posted online on Monday, come on the heels of clinical trial results indicating that the vaccine fared poorly in children aged 2 to 4 years, who received an even smaller dose.
Public health experts worried that the news would further dissuade hesitant parents from immunizing their children. Other studies have shown the vaccine was not powerfully protective against infection with the Omicron variant in adults, either.
“It’s disappointing, but not entirely surprising, given this is a vaccine developed in response to an earlier variant,” said Eli Rosenberg, the deputy director for science at the New York State Department of Health, who led the study. “It looks very distressing to see this rapid decline, but it’s again all against Omicron.”
Still, he and other experts said they recommended the shot for children given the protection against severe disease shown even in the new data.
“We need to make sure we emphasize the doughnut and not the hole,” said Dr. Kathryn M. Edwards, a pediatric vaccine expert at Vanderbilt University.
