U.S. Measles Cases Rising: Why This Once Eliminated Threat is Back

For decades, measles existed mostly as a memory in the United States, a disease largely consigned to textbooks and history lessons. After the measles vaccine was introduced in the 1960s, cases decreased from millions each year to near elimination. Parents could stop fearing the fever and rash that once defined a pervasive, sometimes deadly childhood illness.

But in recent years, measles has returned in the U.S., with a 25-year high last year of 2,144 cases. As of Friday, 1,136 confirmed cases have been reported so far this year.

According to experts, including Dr. Nicole M. Iovine, an infectious disease physician and hospital epidemiologist at the University of Florida, the resurgence is driven by a simple and dangerous reality: more people are no longer immune. As vaccination rates decline or families delay routine immunizations, even small pockets of vulnerability can allow the virus to spread rapidly.

“You only have to open the door a little bit,” said Dr. Iovine. “And it’s going to come in.”

The Danger of Declining Vaccination Rates

Measles is among the most contagious viruses known. If one infected person enters a room, the virus can linger in the air for up to two hours after they leave. Among unvaccinated people exposed to measles, roughly 90 percent will become infected.

The consequences can be severe, especially for children. About one in five infected children requires hospitalization, according to data from the U.S. Centers for Disease Control and Prevention. About one in 20 kids will develop pneumonia. Others suffer seizures from high fever. In rare cases, about one in every 1,000 infections,  the virus causes encephalitis, a dangerous swelling of the brain that can leave permanent damage. Between one and three children in every thousand infected will die.

“It’s not the common cold,” Dr. Iovine said. “Measles is a serious illness. It can cause permanent harm, particularly in children.”

The MMR vaccine, which protects against measles, mumps, and rubella, is highly effective. Two doses provide about 97 percent protection. But when vaccination rates fall below roughly 95 percent of a population, the protective barrier known as herd immunity begins to weaken, allowing outbreaks to take hold.

That dynamic is now playing out in parts of Florida, where the kindergarten measles vaccination rate is 88.8%, as per the CDC. A recent outbreak at Ave Maria University, located in southwest Florida’s Collier County, infected at least 57 students.

Florida Health Center Responds

At the Healthcare Network of Southwest Florida, a federally qualified health center that serves about 50,000 patients in Collier County, medical leaders moved quickly when measles cases began appearing nearby earlier this month.

“Our medical teams were caring for patients with symptoms consistent with measles,” said Dr. Jaime Khemraj, the network’s chief medical officer. “Because it’s so contagious, we wanted to ensure we were prepared for what could happen next.”

The health center activated an incident command structure, a system more commonly associated with disaster response, to coordinate staff, review treatment protocols and prepare for the possibility of a surge.

They reviewed how to protect healthcare workers, conduct educational outreach, and manage complications such as dehydration, respiratory distress and secondary infections. Children with measles often develop high fevers, sometimes exceeding 105 degrees, which can lead to dangerous fluid loss and seizures.

The Healthcare Network was well-positioned to respond due to its preparation. Roughly 92 percent of its pediatric patients are vaccinated against measles, a rate higher than many surrounding communities. The organization also requires its staff to demonstrate immunity, either through vaccination or testing, ensuring that healthcare workers can safely care for patients during outbreaks.

“Our underserved population was well served by being vaccinated and protected,” Dr. Khemraj said.

Still, preparation did not eliminate uncertainty. Measles outbreaks can escalate quickly, and clinics must be ready to respond to needs beyond their usual capacity.

In anticipation, the Healthcare Network requested additional medical supplies. Direct Relief responded with respiratory medications, antibiotics to treat secondary infections, over-the-counter fever reducers, protective equipment, and hydration products.

“The fact that organizations like Direct Relief can provide medications and supplies gives us the ability to respond almost overnight,” Dr. Khemraj said. “It allows us to care for patients and protect the community if cases increase.”

So far, the clinic has not experienced the overwhelming surge seen in some outbreaks. But physicians remain cautious. Measles spreads most easily in dense settings such as schools, dormitories or households where multiple generations live together.

Children are especially vulnerable. Infants cannot receive their first measles vaccine until 12 months of age, leaving them completely unprotected during their first year of life.

The resurgence of measles, physicians say, reflects not only biology but memory. As the disease became rare, its dangers became easier to forget.

One persistent misconception is that measles is a mild childhood illness. In reality, its complications can be devastating, even in otherwise healthy children.

“It’s a serious, serious illness and it can have really long -lasting permanent damage, particularly in children. I don’t think people know bad measles can be,” Iovine said.

Public health experts emphasize that vaccination remains the most effective tool for preventing outbreaks. When most people are immunized, the virus has nowhere to spread. But when immunity declines, even briefly, measles can reestablish itself with alarming speed.

“We’ve had more than 50 years of experience with this vaccine,” Dr. Iovine said. “It’s one of the safest and most effective vaccines we have. The risks of measles itself are far greater.”