Photo: Bryan Goodchild
Christina Hermos, MD’03, MMSc, hasn’t seen a case of measles since she was doing a fellowship two decades ago. And that was a rare case, involving a child who had arrived from overseas.
Since the measles vaccine was developed in 1963, infections declined to the point that the disease was declared eradicated in the United States in 2000.
But since then, outbreaks of measles have cropped up and spread rapidly among people who aren’t vaccinated.
Why are measles such a concern now?
“Measles is a respiratory virus. It’s incredibly contagious,” said Dr. Hermos, associate professor of pediatrics and chief of the Division of Pediatric Infectious Diseases at UMass Chan Medical School. “If an under- or unvaccinated population is exposed to someone with measles, there is a 90 percent chance for a susceptible person to get infected.”
Before the measles vaccine, “pretty much everybody” got infected, Hermos said. Even if only a small percentage had complications, a large number of children became very ill. “The complications were quite severe, including pneumonia, terrible ear infections to the point that the eardrums would rupture and the kids would have permanent hearing loss, and then the really scary ones, like brain inflammation [encephalitis] and death.”
As of early March, the CDC reported more than 220 measles cases in the U.S. in 2025, with more than 200 confirmed cases occurring in West Texas and neighboring New Mexico. Most of those infected were unvaccinated. Two people, a 6-year-old unvaccinated child and an adult, have died.
Hermos explained what people need to know about the measles vaccine to keep them safe from this highly contagious disease.
How do we know measles vaccines are safe?
Every medication, including vaccines, goes through Phase I, Phase II and Phase III clinical trials before they are approved, Hermos said. After preclinical testing, Phase I trials test the vaccine in a small group of volunteers to evaluate safety and identify side effects. Phase II trials take place in a larger group to further evaluate safety and effectiveness. Phase III trials involve much larger groups—more than 1,000 people—and compare effectiveness against standard treatment while further monitoring safety.
Medications continue to be studied after being approved for the general population. An adverse event reporting system provides real-time safety information.
“Vaccines are more studied than any other approved medication because they’re also given so much more widely,” said Hermos. “The measles vaccine has been used and therefore studied many times more than, say, statins used to lower cholesterol.”
What is the schedule for giving the measles vaccine?
In 1971 the measles vaccine was combined with vaccines for mumps and rubella, forming the MMR vaccine. Children receive one MMR dose at age 1 and another around age 4, before they enter kindergarten. Some parents have expressed concern about young children receiving several vaccines in a short time.
“The schedule was developed based on how it works best with host immunity,” said Hermos. “We know how the immune system responds, and the schedule was extensively studied to select what works best when the vaccine is given along with previously approved vaccines.”
For example, a 2-month-old child may get up to eight vaccines at a visit, based on CDC guidelines. “People talk about ‘overloading’ their kid’s immune system,” Hermos said, “But that’s less of a challenge to their immune system than falling on a sidewalk and scraping their knee.”
Why are some people hesitant to have their child vaccinated?
Hermos said people may avoid vaccines for various reasons. Although no mainstream religion opposes vaccination, some religious groups shun modern medicine or engaging in the health care system in general. The outbreak in Texas is tied to a Mennonite community that has a high rate of religious exemptions for vaccination. The Orthodox Jewish community in New York has seen measles outbreaks.
Certain immigrant communities have also been targeted by people opposed to vaccines. And there are pockets of people who embrace alternative care, sometimes promoted through social media.
“The conversation becomes a needs assessment, and you have to listen to where the family is coming from,” Hermos said. “My pediatric primary care colleagues and I will tell them that vaccines are safe, they’ve been extensively studied, and they prevent deadly diseases. Then you assess what their fears are.”
A notorious case that sparked widespread fear is the since-retracted and discredited 1998 article by Andrew Wakefield, published in the journal, The Lancet, which fraudulently linked the MMR vaccine to autism.
“We could talk about the 16 studies that have disproven any association with vaccines,” said Hermos. She points to one in which researchers looked at younger siblings of children who have autism because there is a genetic component. In families that chose not to give siblings the MMR vaccine, they saw higher rates of autism than the families that did choose to vaccinate.
Hermos said, “MMR is one of the most studied and safest interventions on the planet. I want to remind people what a terrible disease measles is. If it doesn’t kill, it can certainly permanently injure and cause developmental delays and/or deafness. It’s incredibly contagious. And the measles vaccine is close to 100 percent effective.”
Science for Living features the perspectives of UMass Chan Medical School experts on the research behind health news headlines. If you have ideas for topics you’d like to see explored, please send them to susan.spencer1@umassmed.edu.
