Update (May 23): Pfizer and BioNTech today announced that unpublished data show the companies’ COVID-19 vaccine is about 80 percent effective at preventing symptomatic infections in children between the ages of 6 months and under 5 years when a third dose is administered at least two months after the first two. While data are still trickling in, the announcement suggests that the three-dose regimen prompts an immune response comparable to that triggered in adults by the existing, two-dose regimen, researchers tell The New York Times.

Update (March 2): New data released yesterday by the Centers for Disease Control and Prevention (CDC) presents a more complete view of the protections that the Pfizer/BioNTech vaccine offers young children, according to the Associated Press. The CDC analyzed pediatric hospitalization rates from April 2021 through January 2022 and found that the vaccine was 74 percent effective at preventing hospitalization among 5- to 11-year-olds and 92 to 94 percent effective at preventing hospitalizations among 12- to 17-year-olds. Because the CDC study includes a greater span of time during which the Delta variant of SARS-CoV-2 was the dominant variant in circulation, experts tell the AP that the Omicron variant is to blame for the steep drop in vaccine effectiveness against infection reported in the New York State Department of Health study.

The Pfizer/BioNTech coronavirus vaccine offers significantly less protection for fully-vaccinated children aged 5 to 11 than it does for the 12 to 17 age group, according to research conducted by the New York State Department of Health and posted as a preprint today (February 28). The study did not measure the effects of the Moderna vaccine or any others; the Pfizer/BioNTech vaccine is currently the only coronavirus shot authorized in the US for use in people under the age of 18.

The study looked at COVID-19 cases in New York that occurred between December 13, 2021 and January 30, 2022, when the highly-infectious Omicron variant dominated. Over that time period, researchers found that vaccine effectiveness against infection dropped from 66 percent to 51 percent among 12- to 17-year-olds and from 68 percent all the way to 12 percent among 5- to 11-year-olds. Protection against hospitalization dropped from 100 percent to 48 percent in the younger group but only from 85 percent to 73 percent in the older group.

See “How Mild is Omicron Really?

“It’s disappointing, but not entirely surprising, given this is a vaccine developed in response to an earlier variant,” lead study author Eli Rosenberg, the deputy director for science at the New York State Department of Health, tells The New York Times. “It looks very distressing to see this rapid decline, but it’s again all against Omicron.”

Children between the ages of 5 and 11 receive two doses of 10 micrograms each—one-third that of the dosage given to everyone over the age of 12. That difference, STAT reports, calls into question whether younger children received the optimal dose and whether additional measures may have offered them better protection. (Pfizer/BioNTech is testing an even lower dose in children younger than 5, and found that two shots did not induce an adequate immune response; the companies are collecting data on whether a third shot sufficiently bolsters immunity.)

“The difference between the two age groups [in the new preprint] is striking,” Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai who didn’t work on the research, tells the Times. “This is super interesting because it would almost suggest that it’s the dose that makes the difference. The question is how to fix that.”

The study authors write in the preprint that “These results highlight the potential need to study alternative vaccine dosing for children and the continued importance of layered protections, including mask wearing, to prevent infection and transmission.”

See “Does Science Support Lifting School Mask Mandates?