An infectious disease specialist, Marietta Vazquez has long been fascinated by the interplay of infections and populations - and how human behavior can affect the epidemiology of diseases.
"To me, the goal of medicine is not to wait for disease and then cure it but to prevent it," said Vazquez, professor of pediatrics (infectious disease) at Yale School of Medicine.
For that reason, her research has focused on vaccines. For highly contagious diseases like measles, vaccination has long been an effective tool in fighting the spread. But this year is on track to become the United States's worst year of measles since 1991. With five months left to go, the U.S. Centers for Disease Control and Prevention has already logged 2,318 cases in 2026, surpassing the 2,289 cases in all of 2025.
Hundreds have gotten sick as a result of outbreaks in states like Arizona and South Carolina, and there have been smaller clusters of cases in other states.
In an interview, Vazquez explains why we're seeing an uptick in cases, who is most at risk, and the most effective strategies for fighting measles.
The interview has been edited for length and clarity.
By the early 2000s, measles was considered "eliminated" in the United States. So, why are there reports of new cases now?
Marietta Vazquez: Like you said, in the 2000s, we declared measles "eliminated," which basically meant there was no continuous transmission of the virus in the U.S. We're seeing more cases today, but the virus itself hasn't changed. How contagious it is hasn't changed. What has changed is that we're seeing a decrease in vaccination rates. As vaccination rates decline, we're seeing an increase not only in the total number of cases, but also in continuous transmission.
How does someone get measles?
Vazquez: Measles is one of the most contagious infections we know of. There's something called the R-naught, or R₀, which is a measure of how many people can become infected when they're exposed to an infectious agent. For measles, that number is very high. About nine out of 10 people who are exposed can become infected. The virus spreads through the air, so it's almost impossible to contain once there's an infected individual who is in contact with others.
What are the complications of measles?
Vazquez: Some people think of measles as a very benign childhood illness. In some cases, individuals might have a cough, congestion, or red eyes, but for many, it can become quite serious and lead to complications such as pneumonia, encephalitis, and even death. Even the most experienced infectious disease specialist can't tell with 100% certainty who's going to have just a rash, fever, and malaise and who's going to end up in the hospital. It's a very serious disease.
Why are young children most at risk for measles?
Vazquez: First and foremost, it's a lack of immunity. When you have a population where the majority of individuals have been vaccinated, that protection can be passed from mother to infant, and it lasts for a few months. It starts to wane around the time infants are vaccinated. So, if we're now in an environment where fewer individuals are getting vaccinated, fewer infants are going to receive that protection. They may have little to no protection, their airways are smaller, and their immune systems are not fully mature. Those are some of the reasons why infants are more at risk. But let me be very clear: It is not only infants that get infected. Anybody can get infected.
What does treatment for measles look like today?
Vazquez: It's a challenge because, after you've been exposed, there's very little we can do to treat the infection. We don't have an effective treatment for measles, so much of the care is supportive. If you're a parent, you shouldn't wait for an outbreak in your community before going to your doctor and asking about vaccination. This infection spreads like wildfire through communities. Waiting for an outbreak is probably not in our best interest if we really want to prevent infection. Prevention is key.
What's the most effective strategy for fighting measles?
Vazquez: It's vaccination. Period. Measles is preventable. We've had a vaccine in the United States for many, many years that works very well. One dose of the measles vaccine is about 95% effective, and two doses are almost 100% effective. It's really the best tool we have for not only preventing disease in individuals but also stopping outbreaks and keeping communities healthy.
How can we better talk to parents about the measles vaccine?
Vazquez: The message has remained consistent for many years: We have a way of preventing measles. The vaccine is safe, the vaccine is effective, and the vaccine is available. Listening to the concerns of patients and parents is also very important. There are a lot of conflicting messages nowadays, and we need to acknowledge that. We need to understand that our patients aren't just going to do what we tell them to do. We're there to make a recommendation, answer questions, and listen. So, a strong recommendation for something that we know works well is very important. But that needs to go hand in hand with understanding and addressing people's questions and concerns.
