'We're already on the precipice of disaster': Deadly measles outbreaks could explode across the US in the next 25 years if vaccinations fall, model predicts

Measles was eliminated in the U.S. decades ago, but millions of new measles cases could pop up across the country over the next 25 years if vaccination rates continue to fall, new modeling suggests.

In a study published Thursday (April 24) in JAMA, scientists forecasted the number of measles cases that might be seen in coming decades if state-level vaccination rates stay steady, decline or increase. If vaccination rates drop by 10%, they found, there could be 11.1 million cases of measles across the U.S. in the next 25 years.

If vaccination rates stay the same as they are today, 851,300 cases of measles could occur in the same timeframe. In that scenario, the disease could feasibly "reestablish endemicity" within about two decades, meaning it could start to spread consistently in the U.S. once more.

If vaccination rates dropped as low as 50% of current levels, 51.2 million cases of measles could occur in the coming 25 years.

Related: When will the US measles outbreak end?

Assuming the rates of all routine vaccinations fell across the board, that would come with upticks in cases of other diseases, like rubella and polio. All told, this could lead to 10.3 million hospitalizations and 159,200 deaths, the model predicted, along with thousands of cases of post-measles neurological complications, rubella-related birth defects and polio-triggered paralysis. (Like measles, both rubella and wild polio have been eliminated in the U.S.)

"We're already on the precipice of disaster," study lead author Mathew Kiang, an assistant professor of epidemiology at Stanford University, said in a statement. "There really shouldn't be any cases at this point, because these diseases are preventable. Anything above zero is tragic. When you're talking about potentially thousands or millions, that's unfathomable."

Measles is a highly infectious viral disease that can be fatal in some cases. Measles can be prevented using the MMR vaccine, which protects against measles, mumps and rubella, or the MMRV vaccine, which additionally protects against varicella (chickenpox).

According to the Centers for Disease Control and Prevention (CDC), one dose of a measles vaccine is 93% effective at preventing the infection, while the recommended two doses are 97% effective.

Thanks to widespread use of these vaccines, measles was declared "eliminated" in the U.S. in 2000; "elimination" is defined by the CDC as an "absence of continuous disease transmission for 12 months or more in a specific geographic area."

But vaccination rates have been falling, and as a result, the U.S. has seen a major measles outbreak this year. According to the CDC, as of April 17, 800 confirmed cases of measles and three deaths have been reported across 24 states so far this year. Of these cases, 249, or 31%, occured in children under age 5. Another 304 (38%) affected people ages 5 and 19. Nearly all of the people infected — 96% — were unvaccinated or had unknown vaccination status.

Texas has been the hardest hit state, with 624 cases reported as of April 22, according to state-level data. Of those, 602 occurred in unvaccinated people or those with unknown vaccination status.

Vaccination rates across the U.S. have been dropping significantly in recent years. Measles outbreaks are prevented by herd immunity, which describes when enough of the population is immune to a disease to prevent its spread. For measles, you hit the herd-immunity threshold when 95% of the population is fully vaccinated.

But between the 2019-2020 school year and the 2023-2024 school year, the percentage of kindergartners who had received two doses of the MMR declined from 95.2% to 92.7%. (Children are recommended to get a dose of a measles vaccine between the ages of 12 and 15 months and a second dose between 4 and 6 years old.)

"We've seen a worrisome pattern of decreasing routine childhood vaccinations," study co-author Nathan Lo, an assistant professor of infectious diseases at Stanford University, said in the statement. "People look around and say, 'We don't see these diseases. Why should we vaccinate against them?' There's a general fatigue with vaccines. And there's distrust and misinformation about vaccine effectiveness and safety."

This anti-vaccine sentiment has been egged on by a variety of public figures, including the current Secretary of the U.S. Department of Health and Human Services Robert F. Kennedy Jr., who has a history of promoting unsubstantiated claims linking vaccines to autism, despite a robust scientific consensus debunking these claims and affirming vaccine safety and efficacy.

The new study modeled how measles cases would increase if childhood vaccination rates continue to drop over the coming decades. The scientists found that, if vaccination rates remained the same as they were on average between 2004 and 2023, measles would become endemic — consistently present and regularly transmitted — in the U.S. within 20 years. That would lead to 851,300 cases, 170,200 hospitalizations and 2,550 deaths from measles over the next 25 years.

The study highlighted the potential dangers of not only declining MMR vaccination rates, but also falling rates for other routine vaccinations. Infection and death aren't the only outcomes of these preventable illnesses; they can also cause dangerous knock-on complications.

"While the effects of declining vaccination won't be immediate, we could eventually see the return of awful complications from diseases that most clinicians today have not encountered thanks to decades of successful immunization," Lo said.