The Pfizer-BioNTech vaccine’s ability to prevent coronavirus infections in children 5 to 11 years old waned over time although the shot continued to protect against the most serious outcomes, including hospitalization and death, even as omicron surged, newly released data shows.
The data are broadly consistent with real-world effectiveness data for adults showing that protection from two doses diminishes over time, but that in people eligible for a booster, a third dose revs the immune system back up to robust levels. In children, as with adults, vaccine effectiveness faded during omicron and generally decreases relative to the time since vaccination.
The research provides an evolving picture of the vaccine’s performance in children, and some experts said it suggested a need to consider increasing the size of the dose 5-to-11-year-olds receive.
Pediatric infections and hospitalizations reached their highest rate in January, when omicron swept the country. Its higher transmissibility meant more people — including the vaccinated — were likely to be infected. Despite this increase in infections and hospitalization, data show coronavirus vaccines continued to protect 5-to-17-year-olds against severe illness, hospitalization and death.
The Pfizer-BioNTech vaccine is the only shot authorized for children 5 to 11 in the United States. That group receives a 10-microgram dose while those 12 and older get 30 micrograms.
“We knew from the adult data that’s been published previously that the vaccine provides less protection versus omicron than it did against delta, and I think we’re continuing to see that pattern in children,” said Ruth Link-Gelles, who leads CDC’s team on effectiveness of coronavirus vaccines.
“We also know from the adult data again that vaccine provides much better protection against severe disease. And we are seeing, I think, that same pattern in children,” Link-Gelles said.
Experts said the message for parents is that even if vaccine efficacy declines over time, “it is still better than being unvaccinated, and it is better for you to vaccinate your children,” said John P. Moore, a professor of microbiology and immunology at Weill Cornell Medicine.
Link-Gelles, who has a daughter not yet eligible for vaccination, said she found the data reassuring.
“Every time there’s a new variant, we worry that the vaccine will provide no protection at all,” Link-Gelles said. “And that is certainly not the case here. … The infection cases are less concerning to me as a parent. What I want to avoid are midnight emergency room visits, hospitalizations and, obviously, death. And I think that these data do show that we’re continuing to see protection against those outcomes.”
Jesse Hackell, a pediatrician in Rockland County, N.Y., said his advice to parents will remain the same.
“The vaccine is extraordinarily safe, and it protects against the rare but serious illnesses,” Hackell said in an email. “There is no downside to giving it, even if the efficacy is less than hoped — one is STILL better off having had the vaccine than not, even if the benefit is smaller.”
The latest data on efficacy in 5-to-11-year-olds come after developments involving shots for children younger than 5. The Food and Drug Administration in January said it would review data for a two-dose regimen in hopes of swift authorization and then add a third dose after data on a booster became available.
But the agency reversed course in mid-February, after receiving disappointing data on two doses. It announced it would not make a decision on whether to authorize a coronavirus vaccine for children younger than 5 until data on a third dose becomes available. That means the vaccine is unlikely to be available until at least mid-April.
Some experts said the recent findings raise additional questions about the dose needed for younger children. Data from New York state “strongly suggest that the lower vaccine dose given to 5-to-11-year-olds is not inducing the strong protective immune responses we see in older children and adults,” said Albert Ko, an infectious-diseases physician and epidemiologist at the Yale University School of Public Health.
The data “doesn’t feel settled,” said Natalie E. Dean, an Emory University biostatistician. “This may well be a three-dose vaccine. … We’re still piecing this together. It’s going to take a few more studies.”
The CDC released two analyses Tuesday. One report evaluated the protection afforded by the Pfizer-BioNTech vaccine against emergency department and urgent care visits in 10 states from April 2021 through January. It showed the vaccine was protective against hospitalization and death in 5-to-17-year-olds, even after omicron emerged.
Among the findings:
— After two doses, the vaccine initially was 92 percent to 94 percent effective for 12-to-17-year-olds against hospitalization during the delta and omicron waves. But protection against hospitalization faded more than five months after getting the second shot, with effectiveness falling to a range of 73 percent to 88 percent.
— Children 5 to 11 years old were not eligible for vaccine until early November 2021 so did not become fully vaccinated until mid-December, as omicron surged. Twenty-three vaccinated children were hospitalized with covid-like symptoms during the study period, but only two were infected. By comparison, 262 unvaccinated children were hospitalized, and 59 were infected.
— Two doses of the vaccine were about 51 percent effective in preventing 5-to-11-year-olds from going to emergency departments and urgent care centers as omicron spread, the CDC study found. For fully vaccinated 12-to-17-year-olds, protection ranged between 34 percent for older teens and 45 percent for younger adolescents for the same period. For older teens who received boosters, protection rose to 81 percent.
In a separate CDC analysis of surveillance data from 29 jurisdictions, vaccinated children and adolescents were less likely to be infected than those who were unvaccinated, despite a decline in protection against infection during the omicron surge. Unvaccinated 5-to-11-year-olds were 1.3 times more likely to get infected during January, compared with those who were vaccinated; unvaccinated 12-to-17-year-olds were 1.5 times more likely to get infected.
That analysis identified nine covid deaths in vaccinated children 5 to 17 years old between April 4, 2021, and Jan. 1, compared with 121 deaths among unvaccinated children.
New York state data released Monday, which is about one-tenth the size of the population analyzed in the CDC surveillance data, showed a rapid and steep drop in vaccines preventing infection in 5-to-11-year-olds compared with adolescents.
The New York study analyzed health records for covid cases in children and teens from Dec. 13, 2021, to Jan. 30. During that period, protection against infection from a two-dose regimen for 5-to-11-year-olds fell from 68 percent to 12 percent. Protection against hospitalization fell from 100 percent to 48 percent.
In the New York study, protection against infection for 11-year-olds was much lower compared with children a year or two older, possibly because the 11-year-olds received the 10-microgram-dose, while the older children received 30 micrograms.
If the findings are replicated in other settings, the researchers wrote, “review of the dosing schedule for children 5-11 years appears prudent.”
New York State Health Commissioner Mary T. Bassett said in a statement the data are not surprising because the vaccine was developed in response to an earlier version of covid and “reduced effectiveness of 2 doses against the omicron variant has been seen to some degree with all vaccines and ages.”
Bassett said it was critical to stress that vaccination is still recommended for everyone 5 and older.