By Amir Obeid, Georgia-Leigh Hewitt, and Philip R. Fischer, MD
Synopsis: Several measles outbreaks have been active in the United States, with more than 1,000 cases reported already in 2025. Most outbreaks begin as unvaccinated individuals in the United States come into contact with an infected individual who has recently arrived after international travel. Vaccination is effective, but current U.S. vaccine coverage rates are below the 95% rate considered necessary to provide herd immunity.
Sources: Mathis AD, Raines K, Filardo TD, et al. Measles Update — United States, January 1-April 17, 2025. MMWR Morb Mortal Wkly Rep. 2025;74(14):232-238.
Centers for Disease Control and Prevention. Measles cases and outbreaks. May 16, 2025. www.cdc.gov/measles/data-research/index.html
Within the first 16 weeks of 2025, the number of measles cases in the United States has risen quickly, causing both local and national concern. To monitor the current situation, accurate and efficient reporting systems are used. The Centers for Disease Control and Prevention (CDC) is notified of confirmed cases by state health departments either directly or through the National Notifiable Diseases Surveillance System. Subsequently, understanding the epidemiology of these cases is critical to developing successful interventions.
A total of 800 confirmed cases of measles were reported between Jan. 1 and April 17, 2025, in 25 U.S. jurisdictions. (The CDC updates their measles data every Friday. As of May 16, 2025, the total number of confirmed cases in 14 outbreaks is 1,024 in 31 U.S. jurisdictions.) The median age of affected patients was 9 years. Among these individuals, 771 (96%) were unvaccinated or had unknown vaccination status. Of the 800 cases, 790 (99%) occurred in U.S. residents and 85 (11%) were hospitalized. Three confirmed deaths were reported to the CDC, two in unvaccinated children in Texas, and one in an unvaccinated adult in New Mexico. More than two-thirds of cases [557 (70%)] were confirmed by laboratory testing.
Of the affected patients, 44 cases (6%) were in U.S. residents who had traveled to other countries and four were in international visitors to the United States, while 753 (94%) infections were acquired in the United States. Among the imported cases, 33 (69%) were unvaccinated, all of which were age-eligible for vaccination according to the Advisory Committee on Immunization Practices. The countries from which most imported cases arrived included Canada, Vietnam, and Mexico.
Among the confirmed measles cases, 751 (94%) of them are associated with the 10 outbreaks identified throughout the country. Seven outbreaks had an imported source, while the rest remain without an identified origin. The largest outbreak began in an under-vaccinated, isolated community in Gaines County, TX, in January 2025. This unsourced outbreak alone accounted for 654 (82%) cases reported in 2025 and the majority of the cases in Texas, New Mexico, and Oklahoma. Within this geographical area, close-knit communities that often do not access healthcare typically are unvaccinated; many of the cases reported are from within these communities. Furthermore, an infected Mexican resident who returned from Gaines County, TX, has reportedly resulted in an outbreak in Chihuahua, Mexico.
Commentary
The current outbreak between New Mexico, Oklahoma, and Texas is the largest since elimination was declared in the United States in 2000. More concerning, it is inferred that cases currently are underreported — both because of unknown sources of infection and since communities at risk often do not seek healthcare.
Yet, there are actions all stakeholders can take. Healthcare providers are urged to maintain a high level of suspicion of measles in their patients presenting with typical symptoms and travel to areas both within and outside the United States with higher rates of measles. Public health officials and clinicians should ensure that all patients traveling abroad are adequately immunized, as well as prepare each region for testing and reporting. They also must establish partnerships with communities at high risk. Since these groups have reserved trust in healthcare systems, culturally competent strategies are needed to increase both vaccination rates and access to healthcare if infection is suspected. Using the knowledge of community leaders who then can distribute information is vital.
Above all else, immunization rates across all communities must increase above 95%, the threshold for herd immunity. Efforts must be made on local and national levels to fight against the tide of decreasing immunization rates across the country, otherwise the country is at great risk of losing its status of having eliminated measles.
The current measles outbreaks in the United States are concerning acutely for affected patients and families and communities. Coupled with declining vaccination rates, the current measles outbreaks also indicate the risk that 25 years after measles was eradicated, it will again become endemic within the United States. At the same time, the rest of the world also is struggling with measles. The three measles deaths in the United States this year are tragic, but there are more than 100,000 measles-related deaths each year in the rest of the world.
The clinical presentation of measles is well-described, even if it is no longer commonly seen by physicians.1 About a week after exposure, the patient develops fever, runny nose, cough, and conjunctivitis. After four days of illness, a rash appears. Fever can last eight days. Pulmonary involvement is common, and secondary bacterial pneumonia can be fatal. Neurologic complications (acute encephalopathy and subacute sclerosing pan-encephalitis) are rare but potentially devastating.
As demonstrated by the majority of the 2025 measles outbreaks in the United States, initial infection often arrives with an international traveler and then spreads through unimmunized members of the local community. The index patients identified in outbreaks have come from Canada, Europe, Africa, and Asia. Restricting travel is unlikely to be an effective control strategy, but widespread immunization would be effective.
Rates of measles immunization are down to about 91% in the United States and dropping.2 This is significantly below that 95% coverage that Mathis et al believe can provide enough herd immunity to prevent measles from reestablishing itself as endemic in the United States. Others suggest that 92% to 94% vaccination coverage might be enough, but even that coverage is not currently being achieved in the United States.2 Recent data from Stanford University suggest that there could be more than 800,000 measles cases in the United States over the next 25 years if immunization rates hold at their current level, and millions more cases if immunization rates continue to decline.3,4
Vaccines are effective. A single dose given between 6 and 12 months of age can protect children whose maternally acquired measles antibodies have waned. A single dose at or after 12 months of age protects approximately 93% of children. A second dose at least a month after the first leads to approximately 97% protection. In addition to stimulating humoral immunity, measles vaccines also prompt cellular immunity. Thus, even as post-vaccine antibody levels wane slightly during the decade after immunization, vaccination actually seems to provide life-long protection to well over 99% of recipients.5,6
Measles vaccines are available and are protective. The controversy about the safety of the measles vaccine is recognized, but numerous controlled, peer-reviewed studies have not supported any of the many negative claims. The current measles vaccine has been proven to be very safe and the best way to prevent measles and complications, including deaths from measles. Focusing on any lesser means of reducing cases of and deaths due to measles, according to one former president of the Infectious Diseases Society of America, would be silly. “Imagine,” he said, “if the captain of the Titanic had told you that you need to be careful about lifeboats and think about other opportunities.”7 The current measles outbreaks pose the risk of measles again becoming endemic in the United States. We (and our public health and political leaders) must not lose sight of the currently available solution — routine vaccination of children and vaccination of under-immunized adults and travelers.
Amir Obeid and Georgia-Leigh Hewitt are medical students at Khalifa University College of Medicine and Health Sciences in Abu Dhabi, United Arab Emirates.
Philip Fischer, MD, DTM&H, is Professor of Pediatrics, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN.
References
1. Li CN, Kaplan SL, Edwards KM, et al. What’s old is new again: Measles. Pediatrics. 2025. doi: 10.1542/peds.2025-071332.[In press].
2. Bednarczyk RA, Sundaram ME. The continued risk of measles outbreaks in the United States resulting from suboptimal vaccination coverage. Public Health Rep. 2025;Jan 3:333549241306608. doi: 10.1177/00333549241306608. [Online ahead of print].
3. Kiang MV, Bubar KM, Maldonado Y, et al. Modeling reemergence of vaccine-eliminated infectious diseases under declining vaccination in the US. JAMA. 2025; Apr 24:e256495. doi: 10.1001/jama.2025.6495. [Online ahead of print].
4. Mullin E. Scientists find measles likely to become endemic in the US over next 20 years. Wired. April 24, 2025. www.wired.com/story/scientists-say-measles-likely-to-become-endemic-in-us-polio-diphtheria-rubella/
5. Lutz CS, Nguyen HQ, McClure DL, et al. Patterns in decline in measles, mumps, and rubella neutralizing antibodies and protection levels through 10 years after a second and third dose of MMR vaccine. Open Forum Infect Dis. 2025;12(4):ofaf188.
6. Rivard KR. Does my adult patient need a measles vaccine? Cleve Clin J Med. 2025;92(5):279-282.
7. Seitz A. RFK Jr.’s mixed message about the measles outbreaks draws criticism from health officials. Associated Press. April 16, 2025. https://apnews.com/article/measles-outbreak-rfk-jr-messaging-criticism-vaccine-1a2cbdc14eb0c256695fdfac00cbfb6d
Several measles outbreaks have been active in the United States, with more than 1,000 cases reported already in 2025. Most outbreaks begin as unvaccinated individuals in the United States come into contact with an infected individual who has recently arrived after international travel. Vaccination is effective, but current U.S. vaccine coverage rates are below the 95% rate considered necessary to provide herd immunity.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content