Before the introduction of vaccines, childhood diseases often led to severe health issues or even death. Thankfully, vaccines transformed many of these once-common illnesses into mere pages in medical textbooks.
However, when vaccination rates decrease, we risk seeing a resurgence of these diseases. Take measles, for example; it has reemerged in communities where parents have chosen not to immunize their kids.
Now, consider the scenario where even those who wish to vaccinate their children can’t access the vaccines.
Health Secretary Robert F. Kennedy Jr., who has founded an antivaccination organization, is contemplating changes that could possibly lead to a situation where the few companies that provide vaccines for American children stop supplying them. Over the past year, he has shifted the narrative from one that promotes the critical importance of vaccinations to one that questions their safety—both domestically and globally.
After Kennedy’s nomination, some experts began speculating about his potential impact on America’s vaccination policies. Researchers from Stanford University were curious about how many individuals might be at risk if vaccination rates fell or if shots became completely unavailable for four significant diseases: polio, measles, rubella, and diphtheria.
Outbreaks often originate when someone contracts these illnesses abroad and returns home. To assess this, epidemiologists Mathew Kiang and Nathan Lo, who specializes in infectious diseases, created a model to simulate the spread of these four diseases based on varying vaccination rates across states.
Since a good portion of the population is currently vaccinated, these diseases likely wouldn’t spread immediately. However, as more unvaccinated babies are born, vulnerability increases among the population.
The scholars conducted thousands of simulations for each disease, leading to estimates of potential deaths and disabilities over a 25-year timespan.
Their findings indicate that, at current vaccination levels, the nation is very close to a significant spike in measles cases—a spike that could be almost entirely averted with just a 5% rise in vaccination. Conversely, if vaccination rates were to be halved, all four diseases could make a comeback.
The worst-case scenarios they projected assumed a 25-year period where vaccines were entirely inaccessible, not factoring in possibilities such as parents seeking vaccinations abroad or governmental intervention to encourage manufacturers to provide them.
Yet, these results starkly highlight how crucial vaccines are and the consequences of policy changes that could hinder American parents from immunizing their children.
ProPublica communicated the primary findings of this scenario to the Department of Health and Human Services. An agency spokesperson did not specifically address the modeling results but asserted that “HHS has not limited access or insurance coverage to any FDA-approved vaccines” and continues to advocate for routine vaccinations for children.
When their study was published in early 2025, Kiang and Lo emphasized potential outcomes from less dramatic declines in vaccination rates, as peer reviewers deemed these scenarios more plausible. At that time, Kennedy had just begun his role at HHS.
A year later, however, the idea that vaccines might become inaccessible seems increasingly conceivable, according to Kiang. “Every passing week,” he remarked, “this feels more likely.”
Lo pointed out their intention was to illustrate to policymakers the potential consequences of their decisions.
This led ProPublica to illustrate a possible future in which vaccines are no longer available.
What if we lost
the vaccine for
Measles
Measles is one of the most contagious diseases on record. A child infected can transmit it before even showing symptoms, and the virus can survive in the air for about two hours after an infected person leaves a room.
Known for its distinctive spots, measles is a respiratory ailment that can lead to serious complications like pneumonia and encephalitis. Prior to the vaccine’s availability, measles affected nearly everyone, resulting in 400 to 500 deaths annually in the U.S.
The model estimates that about 3 out of every 1,000 measles infections would result in death.
What if we lost
the vaccine for
Rubella
Rubella, often called German measles, tends to be mild in most people. Yet, it can be catastrophic for a developing fetus. If a mother contracts rubella early in her pregnancy, there’s a substantial risk—up to 90%—that the baby will have congenital rubella syndrome, leading to serious conditions like heart defects, hearing issues, or blindness. Many of these children also face intellectual disabilities, and approximately one-third of them may not survive past their first year. An epidemic in the United States during the 1960s resulted in 20,000 infants being born with congenital rubella syndrome.
What if we lost
the vaccine for
Diphtheria
Historically, diphtheria was a leading cause of death among children, earning it the nickname the “strangling angel.”
The disease’s name derives from a Greek term meaning leather, as its toxin attacks the respiratory system, causing dead tissue to accumulate in the throat, obstructing the airway.
Survivors can still experience severe nerve and heart damage from the toxin. It’s particularly concerning that patients who seem to recover can unexpectedly die weeks later.
An antitoxin derived from horse blood must be administered quickly, but supply issues often occur. In other regions, children have died awaiting this treatment.
Diphtheria is rare today and less contagious compared to measles or rubella. Still, it poses a much greater risk of death. The model estimates that even with only one traveler infected every five years, 10% of unvaccinated individuals who contract diphtheria could die.
The researchers found that while it’s conceivable for no diphtheria deaths to occur over the 25-year model period, losing access to the vaccine places us in a precarious position. The threat of the “strangling angel” resurfacing is real.
Data on paralytic polio cases, measles mortality, congenital rubella syndrome incidents, and diphtheria fatalities are averages from a model developed by Stanford’s Mathew Kiang and Nathan Lo, which executed 2,000 simulations for each of the diseases. When we mention a “range” of possibilities, we’re talking about values within the upper and lower limits of a 95% uncertainty interval—meaning that across all simulations, 95% of the outcomes fall within these parameters. The worst-case estimate for diphtheria deaths used here represents the upper end of this range.
For polio, the model produced an average of 23,066 cases of paralytic polio, with a variation between 0 and 74,934 cases.
The model estimated an average of 290,129 measles deaths, with a range from 285,271 to 294,286 deaths.
For rubella, the average number of congenital rubella syndrome cases was found to be 41,441, with a range from 34,876 to 48,373 cases.
As for diphtheria, an average of 138,284 deaths was determined, with a range spanning from 0 to 1,460,394 deaths.
The vaccination rates taken into account were averages from 2004 to 2023 across the states.
The six reported measles deaths over the past 25 years come from a report by the Centers for Disease Control and Prevention.
Last year, the Stanford researchers, along with others, published a peer-reviewed study in the Journal of the American Medical Association showing possible outcomes from less drastic vaccination declines.
