For generations of Americans, the fear of childhood diseases like polio, measles, and diphtheria is a distant memory, confined to history books and grainy photographs. This victory was earned not by chance, but by one of public health’s most powerful tools: widespread vaccination. Yet this hard-won protection is not guaranteed forever. A new analysis from Stanford University researchers forces us to confront a stark possibility: what if the vaccines that shielded us became unavailable?
The Unthinkable Scenario: A Future Without Vaccines
The question is no longer purely theoretical. Health Secretary Robert F. Kennedy Jr., who has a long history of antivaccination activism, is considering policy changes that could lead the few companies that manufacture most childhood vaccines to cease selling them in the United States. Over the past year, his leadership has shifted the Department of Health and Human Services from a champion of immunization to a voice questioning vaccine safety both domestically and internationally.
To understand the human cost of such a shift, epidemiologists Mathew Kiang, PhD, MS and Nathan Lo, MD, PhD—an infectious diseases physician at Stanford—built a sophisticated model. Their work, published in the Journal of the American Medical Association (JAMA) in 2025, simulates how four once-common diseases—polio, measles, rubella, and diphtheria—could spread if vaccination rates plummeted or shots vanished entirely. Their model is based on real-world state-level vaccination data and the natural dynamics of disease transmission.
How the Model Works
The researchers ran thousands of simulations for each disease, factoring in how outbreaks often begin with an infected traveler returning from abroad. Their model assumes a 25-year period where vaccination rates either decline or drop to zero for new birth cohorts, meaning babies are born into a population with growing susceptibility. The results are presented as average outcomes with a range of possibilities (a 95% uncertainty interval), reflecting the chaotic nature of real epidemics.
When ProPublica shared the grim findings of a complete vaccine loss scenario with HHS, an agency spokesperson stated, “HHS has not limited access or insurance coverage to any FDA-approved vaccines” and continues to recommend routine childhood immunizations. The spokesperson did not directly address the modeling.
What the Numbers Mean: A Disease-by-Disease Look
The model’s projections are a sobering ledger of potential suffering. Here is what a quarter-century without these specific vaccines could mean, based on the researchers’ averages.
Measles: The Contagion That Could Ignite Quickly
Measles is one of the most contagious viruses known. An infected child can spread it before showing a rash, and the virus lingers in the air for hours. Before the vaccine, it was virtually universal, killing 400-500 Americans annually and causing pneumonia and brain swelling.
- Model Average Deaths (25 years): 290,129 (range: 285,271 to 294,286)
The model assumes a fatality rate of 3 deaths per 1,000 infections. Kiang and Lo’s earlier, peer-reviewed work showed that the U.S. is already near a tipping point; a mere 5% drop in MMR vaccination could trigger explosive outbreaks. A 50% drop, as modeled in the worst-case scenario, would allow measles to re-establish itself permanently.
Rubella: A Threat to the Next Generation
While often mild in children, rubella is catastrophic for pregnancies. Infection in early pregnancy carries up to a 90% risk of congenital rubella syndrome (CRS) in the baby, causing heart defects, deafness, blindness, and intellectual disabilities. A third of CRS babies die before age one. The 1964-65 U.S. epidemic left 20,000 children with CRS.
- Model Average CRS Cases (25 years): 41,441 (range: 34,876 to 48,373)
With no vaccine, every susceptible pregnant woman would face this risk. The model’s toll represents tens of thousands of children born with severe, lifelong disabilities.
Diphtheria: The “Strangling Angel” Returns
This bacterial infection was a leading child killer in the early 20th century. Its toxin creates a thick membrane in the throat that can block the airway—hence the nickname “strangling angel.” Even survivors can suffer nerve and heart damage weeks later. The antitoxin is in critically short supply globally.
- Model Average Deaths (25 years): 138,284 (range: 0 to 1,460,394)
The massive range reflects diphtheria’s lower contagion compared to measles. The model assumes only one infected traveler arrives every five years, but with a devastating 10% fatality rate for the unvaccinated who contract it. The high-end of the range—over 1.4 million deaths—is a low-probability but catastrophic outcome from a sustained outbreak. As the researchers note, we would be playing a “game of high-stakes roulette.”
Polio: The Shadow of Paralysis
Polio’s return would be a profound moral failure, as it was the first major vaccine victory. It can cause irreversible paralysis, primarily in children.
- Model Average Paralytic Cases (25 years): 23,066 (range: 0 to 74,934)
Like diphtheria, polio’s lower contagion creates a wide possible outcome range. But even the average—over 23,000 children paralyzed—represents an unimaginable regression.
The Stakes and the Path Forward
These numbers are not predictions; they are simulations of plausible futures based on disease biology and population immunity. They do not account for potential mitigating factors, such as parents seeking vaccines abroad or political intervention to restore supply. However, they serve as a critical warning from expert modelers: if we lose the infrastructure and trust that delivers vaccines, we unlock the door for diseases that modern medicine has held at bay for decades.
“Our goal was to show policymakers, ‘if we make certain decisions, this is what could happen,'” said Dr. Lo. A year after their paper’s publication, with vaccine discourse shifting at the highest levels, Dr. Kiang notes the “no vaccine” scenario “seems more plausible every week that goes by.”
The last 25 years saw only six measles deaths in the U.S., according to the CDC. That statistic is a testament to a system that worked. The Stanford model illustrates what happens when that system fails. It transforms abstract debates about policy into concrete human consequences: hundreds of thousands of dead children, millions disabled, and a nation forced to relive the “plagues from the past” it thought it had conquered.
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Measles is among the most contagious diseases in history. A child can spread it before they even get a rash, and the virus can linger in the air for up to two hours after they leave a room.
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