Somewhere in South Carolina, a child too young for a second dose of the measles vaccine contracted the virus from someone whose parents had decided, for reasons unrelated to medicine, that vaccination was optional. That single decision, multiplied across a school district, then a state, then dozens of states, is how the United States found itself, over the summer, with the worst measles year in 35 years. It is also how an outbreak in one South Carolina community grew, over six months, into the largest single-location measles cluster since the disease was declared eliminated on American soil in 2000 — an elimination status now, embarrassingly, under formal review. It was reported on Tuesday that two unvaccinated people died of measles in Pennsylvania, the first such deaths in the U.S. this year, and the first in Pennsylvania in 35 years.
I have spent my career studying how immune systems, and by extension, whole populations, build walls against pathogens. I know what it looks like when those walls hold. I also know what it looks like when they don’t. This year, they didn’t.
Here is what the Centers for Disease Control and Prevention did not want to say plainly when it released its annual kindergarten vaccination report last week. Coverage for measles, mumps, rubella, polio and whooping cough fell in more than half of American states during the 2025-26 school year. The share of kindergartners with an exemption from one or more required vaccines climbed to 4.2%, up from 3.6% the year before — an all-time high. The agency’s own media statement described this as “a 0.1% decline” in coverage and insisted rates “remained high.” That is technically true but completely beside the point, the public health equivalent of noting that the tide has only crept up a few inches while standing in a basement that is starting to flood.
Do the arithmetic the CDC’s statement conveniently left out. A 4.2 % exemption rate means roughly 155,000 children start kindergarten this year without full protection against diseases that, a generation ago, put American children in iron lungs and coffins. National coverage against measles, mumps and rubella slipped to 92.4%; coverage against diphtheria, tetanus and whooping cough fell to 92%. Both numbers sit well below the 95% threshold epidemiologists have long identified as the point at which a disease as contagious as measles — one infected person can spread it to 12 or 18 others — can no longer sustain a chain of transmission through a population. Below that line, outbreaks are not a possibility. They are close to a certainty.
We are watching certainty play out in real time. More than 2,700 measles cases have been confirmed in the United States this year, already surpassing the total for all of 2025, with months still to go. Ninety-three percent of those cases occurred in people who were not vaccinated. Children under five — some too young to have received their second dose, others unvaccinated by parental choice — account for a fifth of this year’s infections and a disproportionate share of hospitalizations. These are not abstractions to me. They are the predictable outcome of an immune system deprived, by policy rather than by biology, of the training it needs.
What makes this year’s numbers different from the slow, familiar erosion of the past several years is the source of the exemptions. Medical exemptions — children who genuinely cannot be vaccinated — have remained flat at 0.2% for years. Virtually the entire increase is nonmedical: parents invoking religious or personal-belief exemptions for children who could be vaccinated but are not. Exemptions rose in 41 states and Washington, D.C., this year, up from 36 the year before, and nearly half of all states now report exemption rates above 5%. California, Connecticut, Maine and New York have closed the nonmedical exemption loophole outright. Not coincidentally, those states post some of the strongest coverage numbers in the country. A decade of state-by-state natural experiments has already told us what works. We are, in most of the country, choosing not to use it.
This did not happen by accident. Health Secretary Robert F. Kennedy Jr. fired the CDC’s entire vaccine advisory committee in June 2025 and has continued to promote the thoroughly discredited claim linking the MMR vaccine to autism. Days before the new kindergarten data became public, President Donald Trump signed an executive order directing the Departments of Justice, Education and Health and Human Services to push states toward “maximizing parental choices over vaccinations,” including a recommendation, at odds with the weight of the scientific evidence, to split the combined MMR shot into three separate injections.
Twenty-eight states have already said they will disregard federal vaccine guidance altogether and follow the American Academy of Pediatrics instead. That group’s president, Dr. Andrew Racine, put it starkly: Federal leaders have dismissed measles as benign and unavoidable and have spread misleading information about the MMR vaccine. Dr. William Moss, an epidemiologist at Johns Hopkins, was equally direct: If more and more parents choose not to vaccinate their children for non-medical reasons, we will no doubt see a rise in disease outbreaks. We asked for his prediction. We are now living inside it.
None of this is irreversible, which is precisely why the CDC’s complacency is so hard to forgive. State legislatures, most of which reconvene in January, could close the nonmedical exemption loophole, as California, Connecticut, Maine and New York already have, while keeping medical exemptions genuinely accessible for the small number of children who truly need them. School nurses and pediatricians need adequate staffing to follow up with under-vaccinated families in person, not by mailing another form home in a backpack. And medical societies need to stop treating the federal government’s abdication as someone else’s problem and fill the guidance vacuum with a single, trusted, unified vaccination schedule that does not change with the political weather.
Measles does not read executive orders. It does not care which agency issued which news release, or how gently that release chose to phrase a record-breaking failure. It cares only about how many susceptible hosts it can find. Right now, in more than half of American states, we are handing it more than we have in 35 years. The data is public. The remedy is known. What is missing is the will to act before this year’s warning becomes next year’s obituary.
A.J. Russo (dr.a.j.russo@gmail.com) is a retired biology professor at Mount St. Mary’s University in Emmitsburg and the research director at the Mensah Medical Research Institute in Illinois. He is the author of “Vaccine Development and the Understanding of Immunity” (Cambridge Scholars, 2024) and “Vaccines: How They Work, Their History and Their Impact” (Ethics Press, 2026).
