Experts have warned for years that those exemptions collectively drive holes in herd immunity and risk sparking epidemics. Outbreaks in states that allow exemptions have proven them correct. As just one example, more than 300 people in California, six other states, Canada, and Mexico developed measles in 2015 after an unvaccinated child caught it from another tourist at Disneyland. That outbreak led California to tighten the loopholes in its school requirements—and probably paved the way for the state to be one of just a handful that will require Covid vaccination for school kids when the next academic year begins.

More states have gone the other way, ruling out any Covid mandates for schools—and beyond that, the politically motivated furor over the Covid vaccine has triggered unnerving reconsiderations of all child vaccines. Last summer, the Tennessee Department of Health fired its top vaccination official for reminding local health departments that teens can be vaccinated without their parents’ consent. Last fall, a Florida state senator threatened to review school requirements for vaccines other than Covid. The Georgia General Assembly is currently considering a bill, cosponsored by 17 Republican state senators, that would prevent any government entity, including public schools, from requiring any vaccinations.

Two weeks ago, the independent UK-based polling firm YouGov found that, among a sample of 1,500 US adults, 71 percent support requiring children to be vaccinated against measles, mumps, and rubella, and 55 percent against other infectious diseases (excluding Covid). In an analysis, the pseudonymous science blogger Mike the Mad Biologist—in real life an infectious-disease microbiologist—points out that those percentages aren’t high enough to create herd immunity, especially against measles, which requires vaccination rates of at least 95 percent.

“There’s a lot at stake,” says Jen Kates, a health policy expert and vice president at the nonprofit Kaiser Family Foundation. “Prior to Covid, there were pockets of communities where parents did not want their kids to have to get a school-mandated vaccine, and they would work to get exemptions. But if well-established mandated routine vaccination will be threatened, that would be concerning, because those school mandates are responsible for keeping vaccination rates high among kids and preventing outbreaks.”

It’s against this backdrop of delayed vaccines and increased public scrutiny that the Food and Drug Administration briefly considered authorizing Pfizer’s Covid vaccine for kids ages 4 and under without full trial results—that is, on the basis of data for two doses, not three. (The agency had already asked Pfizer to extend the trial to study the effects of a third dose, but considered moving ahead on partial data to let vaccinations begin anyway.) That plan was abandoned, but it alarmed researchers and may have seeded more doubt among worried parents.

The best outcome, of course, would be for parents and politicians to realize that all vaccinations protect children, and return to supporting all shots wholeheartedly. The next best may be to hope that those objecting to vaccination can make a distinction between the routine shots they have always allowed their children to receive and the new one that has triggered their doubts.

“People’s views are often very vaccine-specific,” says Angela Shen, a vaccine-policy expert and visiting research scientist at Children’s Hospital of Philadelphia, who led the Michigan study and conducts focus groups on vaccine confidence. “What folks are telling me about the Covid vaccine is that the way they feel about it is often not the same thing as what they feel for routine vaccines, for themselves or their children. It’s like a hamburger: You might love the onion but hate the pickles.”


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