There have been at least 733 confirmed measles cases reported across the nation, thelatest datafrom the Centers for Disease Control and Prevention showed Friday.
In just a few weeks, the United States reported four times as many cases than typically seen throughout an entire calendar year, the CDC said.
Before last year, which had a record breaking 2,276 cases, the U.S. averaged 180 cases annually since measles was declared eliminated in 2000.
The record numbers come asSouth Carolinais dealing with the largest outbreak recorded in recent memory.
Other states that have reported cases and are dealing with ongoing outbreaks include Arizona, California, Florida, Georgia, Idaho, Kentucky, Minnesota, Nebraska, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, South Dakota, Utah, Virginia, Washington, and Wisconsin.
Most of the outbreaks occurring across the country are in pockets of under-vaccinated or unvaccinated communities.
"Because it's such an infectious virus, whenever you see measles outbreaks, it in effect, highlights areas of the country or communities in which vaccination rates are low," Dr. Demetre Daskalakis, the former head of the CDC's branch that tracks diseases including measles, told ABC News.
1 year since measles cases found in Texas, US still seeing surge of infections with elimination status at risk
The rate of kindergartners vaccinated with the measles, mumps, and rubella (MMR) vaccine has fallen from 95% in 2019 to below 93% in 2025, CDC data shows. Herd immunity, a threshold for vaccination rates that slow a virus' ability to spread, is typically achieved at 95% vaccination rates, public health experts say.
"I think that this highlights that our defenses are down, especially in some parts of the country and in some communities where vaccination rates aren't high enough to stop measles outbreaks in their tracks," Daskalakis said.
Declining vaccination rates have left approximately 300,000 kindergarteners unprotected from measles infection.
The MMR vaccine is given in two doses, the initial shot given after the first year of life and the second shot given after the fourth year of life.
Low vaccination rates in communities may lead to further outbreaks and spread of the virus, potentially even putting those who are vaccinated at risk.
"If you have someone vaccinated for an infection and expose them to enough of that pathogen, you can overwhelm that immunity," Daskalakis said.
"The lowest hanging fruit strategy to end the measles outbreak is to increase rates of vaccination," he added.
