The number of measles cases in the U.S. has reached a 33-year record high, years after it was officially eliminated in the country, prompting public health experts to sound the alarm that other diseases could experience a similar resurgence.

While measles symptoms typically resolve in a few weeks, the virus can cause pneumonia, making it difficult for patients, especially children, to get oxygen into their lungs. It may also lead to brain swelling, which can cause lasting damage, including blindness, deafness and intellectual disabilities.

According to the US Centers for Disease Control and Prevention, two doses of the MMR (measles, mumps and rubella) vaccine are 97% effective at preventing measles, while one dose is 93% effective. It is uncommon for someone who is fully vaccinated to develop measles, although the first breakthrough case of 2025 was recently detected in Colorado.

Measles cases in the United States are the highest they’ve been since the country eliminated the disease in 2000. The U.S. has reported 1,277 cases since the start of the year, according to NBC News’ tally of state health department data.

With nearly six months left in the year, the total number of cases so far in 2025 has surpassed every year since 1992

Los Angeles, Orange, Riverside and San Bernardino counties have reported eight cases so far this year compared to 10 total in 2024.

While weekly reported cases have slowed over the past few months, the CDC’s figure surpasses the high of 1,274 cases in 2019 and marks a grim milestone for the U.S. as immunization coverage wanes across the country and the federal government’s vaccine policy shifts under Health Secretary Robert F. Kennedy Jr.

The number of reported measles cases in the United States has hit 1,288 in the first six months of this year, the most since the disease was declared eliminated in 2000.