Measles, Once Gone in the U.S., Now Called ‘Canary in Coal Mine’

In early July 2024, a Worcester resident became the one and only confirmed case of measles in Massachusetts that entire year, picking it up during international travel. This year, the highly infectious respiratory virus has yet to rear its head here. But that’s not the case nationwide. A historic surge is now underway in the United States. At the time of this writing, health officials have so far documented 1,454 cases, 180 hospitalizations, and three deaths, including two young children.

If current nationwide vaccination trends continue and no corrective action is taken, measles could once again become a common illness, says research from Stanford’s Division of Infectious Diseases published earlier this year. If that happens, Massachusetts residents and in particular children will be harmed by the disease, which can be fatal to pregnant women and damaging to their babies.

What makes it worse? Measles had once been declared eliminated in the United States, in the year 2000.

Massachusetts has had only eight cases total from 2015 till now, with several zero-case years. This is aided by the relatively high level of vaccination among the state’s residents for the two-dose measles mumps and rubella, or MMR, vaccine. Public officials from Boston’s Department of Public Health have reported that 94% of children in Suffolk County have the full dose. Children under five are among the most likely to have measles-related complications, which is part of the reason MMR vaccinations are a common school-entry requirement. Adults over 20, and pregnant and immunocompromised people are also at higher risk of complications such as pneumonia and brain swelling.

But while those rates of vaccination sound high, for effective herd immunity, closer to 95% or 97% vaccination rates are ideal, said Dr. Adi Rattner Nevo, medical director for Boston Medical Center’s maternal and child health program. Another way to think about it is that at the current rates, 6% of the population could be vulnerable to the disease. This creates a small but still sizable pool of kids in Suffolk County among which an outbreak could potentially spread -- including to immunocompromised individuals who can’t receive the vaccine.

Dr. Adi Rattner Nevo near her office in the South End. Photo by Adam Smith

Rattner Nevo has been collaborating with Boston’s Infectious Diseases Bureau around efforts to reach families in diverse communities that have disparate levels of vaccination. In her work as a family physician, she sees a mix of families who are eager to vaccinate their children, those who are hesitant but still opt for vaccination, and those who do not.

“While we're seeing increased measles rates in the country and around the world, I want people to not feel scared, but rather know that they can take action,” she said. “If they take their kids to their routine physicals, they can get their vaccines for measles that are very safe.” Not only are the vaccines safe, but the 2-dose series has a 97% efficacy rate of preventing measles as shown by multiple peer-reviewed studies. (Contrary to common belief vaccines typically do not offer 100% protection, but the measles jab is particularly effective at preventing the disease.)

'Small Number of People Can Make Difference'

This year, factors including a decline in childhood vaccination rates and an increase in religious exemptions to school vaccination requirements have contributed to measle’s shocking rise nationwide. A model published by Stanford scientists in the Journal of the American Medical Association predicted that if current national vaccination rates of 87.7%-95.6% continue, measles could reach endemicity (meaning regular occurrence) in two decades. In this situation, more people would experience long-lasting health consequences from 850,000 cases over 25 years. With a drastic 10% decrease in vaccination, the research estimates, we could see 11.1 million cases in 25 years. On the other hand, with a 5% increase in vaccination rates, the model predicted less than 6,000 cases and no endemicity in the same time frame.

“This is a really important finding and the more optimistic interpretation that I hold,” said Nathan Lo, assistant professor of infectious diseases at Stanford and a senior author on the study. “Small increases in coverage can reliably prevent measles from returning to endemicity, and only a small fraction of the American people can make the difference.”

Nathan Lo

Matthew Ferrari, a professor of Biology and director of the Center for Infectious Disease Dynamics Penn State who was not involved in the study, agreed with the main findings but cautioned that the model predicts a worst-case scenario to illustrate the importance of vaccination, not the future. To create a model, simplifications to a vast and enormously complex system of disease spread and resulting public health response were made. In particular, the Stanford authors assumed that vaccination rates would drop immediately, whereas in reality they are more likely to taper over several years, providing time for a public health response.

Historically, outbreaks of infectious disease have led to a strong response to tamp down the outbreak. Given the recent turmoil at the Centers for Disease Control and Prevention, including the firing of CDC Director Susan Monarez and the resignation of several high-level leaders amid reported clashes with the Health & Human Services Sec. Robert F. Kennedy Jr.'s  ideology and anti-vaccine rhetoric, this capacity will likely be diminished. This month, Florida is set to drop school vaccination requirements for several highly contagious diseases including chickenpox and meningitis. The MMR vaccine is not on that list, but the shift presents a worrying precedent for vaccination rates.

Ferrari further noted that measles may be the “canary in the coal mine” of reemerging infectious diseases. “Without maintaining routine immunization levels, capacity and support for outbreak response, as long as these pathogens exist globally, measles will lead, but these other pathogens will follow,” he wrote over email. For instance rubella, which was also modeled in the Stanford study, can have horrific consequences for fetuses if a woman is infected early in her pregnancy.

The Covid Effect

A separate investigation from Lauren Gardner’s lab at Johns Hopkins University found that MMR vaccination rates of kindergartners across the United States have fallen after the Covid-19 pandemic. Collecting publicly available data from 33 states at the county-level, researchers found that 78% of counties surveyed had a lower vaccination rate from the pre-pandemic school years (2017-2020) to the post-pandemic ones (2022-2024). On average, the nationwide shift was from 93.9% to 91.3% between those time points. The trend was true but less pronounced in Massachusetts, which had an average pre-pandemic rate of 95.6% and post-pandemic rate of 95.1%, as calculated by the Johns Hopkins’ team’s metrics.

Specific numbers vary by county, and some counties in Western Massachusetts including Berkshire, Franklin, and Hampden have reported kindergarten MMR vaccination at 93.5% or below, averaged over four post-pandemic years. The Nantucket and Suffolk counties similarly have an average rate of around 93% and 94% respectively. Of note, there was a dip in the reported rates statewide from 2020-2022, followed by an increase in 2022-2024. A more in-depth look at data from the Massachusetts government shows significant variation by school. In Franklin County, for instance, MMR vaccination rates ranged from 71%-100% between schools that reported their percentages, while many did not respond.

Of the over 1,400 confirmed measles cases in the United States this year, over 90% had no MMR vaccinations or unconfirmed status, Rattner Nevo highlighted. Current trends indicate that measles and other vaccine-treatable infectious diseases including rubella, polio, and diphtheria may become more frequent disruptions to our daily lives, resulting in school absenteeism and strain on the healthcare system, not to mention being potentially debilitating or fatal. But at least with these diseases, there is a solution.

“As we're already starting to see an increase in Covid cases and flu season is about to start soon, get your vaccine,” Rattner Nevo urged. Symptoms of measles to look out for include a fever, cough, and small red bumps known as the measles rash. “Protect yourself,” she said, “and if you're sick or not sure, then please contact your provider for further guidance.”