, 2025-05-06 06:51:00
Measles was officially eliminated in the United States in 2000. A quarter of a century later, with outbreaks currently underway in several states, the country is at risk of losing its elimination status. And in little more than two decades, measles could be endemic again.
This outcome is not far-fetched but the result of a modeling study led by Stanford University researchers and published in JAMA last month. According to the findings, with current levels of immunization, measles would return to endemic status in the United States within two decades, with more than 850,000 cases in 25 years. A decline in rates of immunization would lead to millions of cases, the researchers said.
The widespread return of measles would pose a challenge to the healthcare system, and in particular to primary care physicians, who would be on the frontline of the epidemic, handling hundreds of thousands of measles cases — if not many millions. “The healthcare delivery system is not prepared for the resurgence of measles,” said Jay Varma, MD, an epidemiologist and primary care physician with Community Healthcare Network, New York City.
The first immediate burden to the healthcare system would be pressure on hospital capacity, similar to what occurred during the height of the COVID-19 pandemic, albeit on a potentially even more serious scale, given that measles is about twice as contagious as COVID-19. Up to 1 in 5 cases of measles could lead to a hospital stay, typically for complications of pneumonia, dehydration, and, in rare cases, encephalitis.
Other challenges would emerge for physicians and healthcare workers, starting with the basics: Disease awareness. “I entered medical school in 1993, and I did not see a single case of measles in all of my medical training,” Varma said. “Most physicians who are practicing today [in the US] have never managed a case of measles.”
The issue is more complex than simply diagnosing a measles rash, he said, or being up to speed on the best and fastest tests to administer. Managing the high virality of measles presents its own set of challenges. For instance, Varma said, clinics may need to stock upon more vaccines than are needed for routine immunization, as well as immunoglobulin, in order to catch up with unvaccinated family members of infected people, and they may not be immediately available.
Doctors and healthcare workers would also be at a higher risk themselves, and possibly without sufficient resources to mitigate risk. Technologies such as air filtration and protective equipment aren’t always widespread, and the concentration of contagious people in crowded spaces, such as urgent care clinics or emergency departments, would expose even vaccinated healthcare providers to additional risk.
With 97% protection on a population basis, the vaccine is highly effective, but being repeatedly exposed to sick people increases the risk of infection. “I don’t worry too much about vaccinated people getting measles,” Varma said. “But I do worry — just like in my home, even if I have a lock on the door and an alarm system, it still doesn’t mean I’m at zero risk if I live in an area where crime has suddenly gotten worse.”
Doctors who treat immunocompromised people would see their patients face additional risks. Further, most patients vaccinated before 1989, when the Centers for Disease Control and Prevention’s Immunization Practices Advisory Committee recommended a two-dose protocol, may have reduced protection.
But the lion’s share of the burden would fall on pediatricians, who treat the most vulnerable patients: Infants.
Particular Risk to Infants
“From my perspective, the real risk of any measles transmission in the US is the risk to infants,” said Nina Schwalbe, PhD, MPH, the CEO of Spark Street Advisors, a health think tank based in New York City.
Infants under a year are typically not vaccinated unless an outbreak is ongoing or they have a specific travel risk, and while maternal antibodies offer some protection, that generally wanes after 6 months. “Infants are definitely at risk even now,” Schwalbe said. “We don’t have to wait 25 years to see the impact of undervaccination on measles and the resulting risk of infant hospitalization. Any transmission poses an immediate and deadly risk.”
For every child who has measles, said Varma, there may be unvaccinated siblings in need of vaccination and additional risks for the youngest patients in pediatric practices. The measles virus is airborne for up to 2 hours and can survive on surfaces for a few hours more, increasing the need for sanitizing medical settings far more thoroughly than with infections such as COVID-19, as measles is much more contagious.
Looming Increase in Long-Term Disability
Measles isn’t only an acute infection. Although rare, it can lead to long-term neurologic sequelae, and with enough cases, their incidence would be significant, too. If the rates of vaccination were halved, the Stanford model found, more than 51,000 children would experience postmeasles neurologic issues.
This would pose additional challenges to clinicians, who would have to be able to reconduct many neurologic symptoms of an earlier measles infection.
“Measles can cause severe neurological complications within a week and months after the diagnosis, and sometimes over a decade after,” Varma said. “The average clinician is now going to have to remind themselves of the varying degrees of neurological complications that include everything from encephalitis to hearing loss to blindness and other conditions.”
The paper also looked at other diseases — polio, rubella, and diphtheria — which would also increase, though not become endemic, under the current vaccination rates. Though their infectiousness is lower, and the caseload would not be comparable with measles, the risk for longer-term disability is higher.
In particular, rubella contracted during pregnancy can cause congenital rubella syndrome — presenting as many potential birth defects and developmental delays — in the child. Diphtheria can cause long-term damage to the lungs, heart, and nerves, with a higher risk for conditions such as breathing difficulties, heart failure, and paralysis. Poliomyelitis can lead to paralysis in as many as 1 in 200 infections. Reduction of current vaccination rates would lead to thousands of long-term disability cases.
Return of Endemic Virus
When it comes to the caseload the United States may see in the next decades and the public health implications, the numbers are striking. Endemicity has several definitions, said Nathan Lo, MD, PhD, an assistant professor of infectious diseases at Stanford University in Stanford, California, and the senior author of the JAMA paper.
The definition the researchers adopted in this modeling considers the benchmark of 100,000 locally acquired cases in a year. At current vaccination levels, endemicity would occur by 2043. Within 5 years from that point, the overall number of cases would surpass 850,000, leading to 170,000 hospitalizations and 2500 deaths, according to the model. This estimate is based on a conservative rate of infection that links each case to 12 more cases, although a single measles case typically causes up to 20 or more.
Should immunization rates follow the pattern of the past few years and continue their decline, the United States would face a disastrous increase in measles infections, the researchers found. A 10% decline over 25 years would lead to over 11 million new cases of the disease. For reference, vaccine coverage declined by 2.5 percentage points between 2019-2020 and 2023-2024.
According to Schwalbe, the findings of the paper are susceptible to changes in policy and can’t be considered highly predictive. “There would be dramatic differences by state. For example, it is difficult to imagine any scenario where New York would change its vaccine schedule or walk back from current policy,” she said. On the other hand, even in states with lower vaccination rates, “once there are more measles and people see the consequences, policy could easily change back, including requiring catch-up campaigns, for instance, in order to attend school.”
Indeed, Lo said variations by state and changes in policy — including potential changes to the current vaccine schedule — would have an important impact on the epidemiology. “States with lower amounts of historical vaccination and immunity are more at risk; that’s pretty straightforward,” in particular when lower vaccination rates are paired with high natality, he said. But risk is higher too in densely populated cities, in particular ones with a lot of tourism and a population exposed to international travelers.
“That increases the chance that someone gets infected with measles internationally and comes back to the US, and because measles is not endemic, the only way outbreaks and endemicity starts is if someone brings measles from another country,” he said.
Yet as caseload increases, differences between states may become less significant. “At a certain point, once you get really high amounts of cases, the entire US is at risk,” Lo said.
But there is good news.
While even a small decrease in vaccination could be catastrophic, Lo said, an even smaller increase in immunization coverage would drastically bring down the caseload to only 5800 over 25 years.
“I think it’s empowering that small percentages of the population can make a positive difference in protecting their communities against measles,” Lo said.
