Posts Misleadingly Omit Critical Data Supporting COVID-19 Vaccines for Youngest Kids

SciCheck Digest

In young children, the Pfizer/BioNTech and Moderna COVID-19 vaccines are expected to primarily protect against severe disease. Both shots successfully met the set benchmarks for vaccine effectiveness, which involved comparing antibody responses to those of adults. Online posts critical of government recommendations for the pediatric vaccines, however, fail to mention these essential data.

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In June, the Food and Drug Administration authorized the first COVID-19 vaccines for young children: a three-dose Pfizer/BioNTech vaccine, for kids 6 months old through 4 years of age, and a two-dose Moderna vaccine, for 6 months through 5 years of age.

Both vaccines, which use messenger RNA, or mRNA, to trigger a protective immune response against the coronavirus, are smaller-dosed versions of the companies’ vaccines for adults, which were found in large, randomized controlled trials to be effective. Real-world evidence also has repeatedly shown the vaccines provide strong protection against severe disease.

As with the authorizations for other children, the primary way the FDA evaluated the COVID-19 vaccines for young kids for effectiveness was through a comparison of the children’s antibody responses to those of adults. If a similar percentage of vaccinated children produce antibodies — and in similar amounts — to vaccinated adults, then it can be inferred that the kids’ vaccine is also effective. This approach, known as immunobridging, is an established method that has been used for other vaccines, including those given to children.

Importantly, the pediatric trials were designed as immunobridging studies from the start — and were not necessarily meant to be able to provide good efficacy estimates of how well the vaccines prevent infection or symptomatic disease.

This is especially relevant because with the rise of the highly transmissible and more immune-evasive omicron variant, scientists don’t expect the vaccines to be very good at averting infections or mild illnesses. Instead, the vaccines are primarily useful in preventing severe disease.

An online post critical of the shots for young children, however, misleadingly skips over all of that. Instead, it calls Pfizer’s and Moderna’s data “extremely weak” and “inconclusive” and only mentions the lackluster or uncertain efficacy estimates from the studies, which were conducted during the omicron era.

“In the subgroup of children aged six months to two years, the trial found that the vaccine could result in a 99% lower chance of infection—but that they also could have a 370% increased chance of being infected,” the post said about the Pfizer/BioNTech vaccine. “In other words, Pfizer reported a range of vaccine efficacy so wide that no conclusion could be inferred. No reputable medical journal would accept such sloppy and incomplete results with such a small sample size.”

The piece, which was a July 14 guest post on former New York Times opinion columnist Bari Weiss’ Substack page, went on to feature Moderna’s efficacy figures, which it called “very weak” or “low.”

The reported efficacy numbers are correct (or nearly so — one of the Moderna figures is not the primary efficacy number). But as we said, that was not the only or even the main information regulators and outside experts used to evaluate the effectiveness of the vaccines. And as a former FDA official told us, focusing on those numbers misses the point. 

“The critical thing in this is that even if the vaccines aren’t very effective in protecting against mild disease … that doesn’t mean they won’t be effective in protecting against severe disease,” Dr. Philip Krause, former deputy FDA chief for vaccines, said in a phone interview. “That was really the FDA’s goal in making the vaccines available.”

The Substack post was co-authored by Dr. Marty Makary, a surgeon and public policy researcher at the Johns Hopkins School of Medicine who has previously spread misleading or unsupported information about COVID-19, and Dr. Tracy Beth Høeg, a physical medicine and rehabilitation physician in private practice in California. Høeg is also a consultant epidemiologist for the state of Florida, which is the only state to recommend not vaccinating healthy children against COVID-19.

The post was subsequently shared on social media and picked up by Fox News’ Tucker Carlson, which spawned additional posts.

Vaccine Immunobridging

On Twitter, Makary criticized the use of “immunobridging,” saying there was “no justification to bypass rigorous safety & efficacy clinical trials in children.”

But as we’ve explained in our guide to the COVID-19 vaccines for the youngest children, the plan from the start was to use immunobridging to infer that the COVID-19 vaccines would work similarly well in children as adults.

“The FDA established with the companies immunobridging criteria to show that the immune responses in these children would be at a level that would likely give comparable protection to what was observed in older people,” said Krause. “And that’s something that’s been done for many other vaccines.”

Immunobridging between children and adults has been used to approve Vaxchora, a cholera vaccine, Krause said, and the method was also used to approve two HPV vaccines down to age 9. Immunobridging from a different flu vaccine tested in children also served as the basis for approving the seasonal flu vaccine Afluria in kids, he added.

“Immunobridging is a common way to extend an existing vaccine into new populations,” Natalie Dean, a biostatistician at Emory University who specializes in methods evaluating the effectiveness of vaccines, told us in an email. “We leverage the extensive efficacy and safety data from other populations, and so do not need to start from scratch in generating evidence.”

Dr. Paul A. Offit, a vaccine expert and pediatrician at the Children’s Hospital of Philadelphia and a member of the FDA’s advisory committee, previously told us that the large confidence intervals for the Pfizer/BioNTech vaccine’s efficacy figures meant that little could be concluded from them — but that the antibody data was “excellent” and “enough” to know that the vaccine is likely to work.

He confirmed to us that the data that “convinced” the FDA to authorize the COVID-19 vaccines for little kids was the immunobridging data.

“Specifically, that the titer of neutralizing antibodies found after vaccination was virtually identical to those titers found in the 18-25-year-old age groups where protection against severe disease was excellent,” he said in an email.