Measles: An Old Foe Has Returned
Texas is experiencing its largest measles outbreak in 30 years and the Centers for Disease Control and Prevention's (CDC) Epidemic Intelligence Service is providing support there. Here is an overview on testing, disease presentation, and vaccination, as well as commentary on the public health impact of vaccine hesitancy, and the unintended consequences of the immunization program’s success.
This photograph depicts a child who was infected with the measles during a US outbreak in 2024. The child’s cheek shows the characteristic rash associated with this viral infection.
Image credit: CDC/ Tatiana Lanzieri, MD, MPH
As of March 7, 2025, Texas is experiencing a significant measles outbreak, with 198 confirmed cases across more than 9 counties, primarily in the South Plains region. This marks the state's largest outbreak in 30 years. Tragically, an unvaccinated school-aged child has died—the first measles-related death in the US since 2015. The outbreak has predominantly affected unvaccinated children aged 5 to 17. Approximately 23 patients have been hospitalized due to complications. The outbreak's spread has been linked to declining vaccination rates, particularly in communities with higher exemption rates. The outbreak is ongoing, and data will be updated each Tuesday and Friday.1
Nationally, the Centers for Disease Control and Prevention (CDC) report 222 measles cases in 2025, with 93% associated with outbreaks. In 2024, there were 285 cases, with 69% linked to outbreaks. Health officials strongly recommend ensuring vaccinations are up to date to prevent further spread of the disease. The measles, mumps, and rubella (MMR) vaccine is highly effective, with 2 doses providing 97% immunity against measles.2
What is Measles?
Most medical experts acknowledge that measles may be the most contagious known infectious disease in humans. It is estimated that an infected carrier can transmit the measles virus to 12 to 18 others, an epidemiological concept known as the basic reproduction number (RO). This RO assumes others are susceptible to the disease and have no existing immunity towards it. This translates to a staggering estimate that nine out of ten unimmunized individuals who are in contact with an infected person will be infected. Central to its infectivity is that the virus can linger in the air for up to two hours after the infected patient leaves a room. Thus, direct contact with or facing an infected person is not necessary for the virus to propagate; a susceptible person simply needs to be in the same room that an infected person was previously in recently.3
Measles virus is a member of the genus Morbillivirus of the family Paramyxoviridae and exhibits a typical incubation period averaging 10–14days from exposure to onset of initial symptoms. The first set of symptoms to occur are typically high-grade fever (>102°F or > 39°C), sinus congestion, cough, myalgia, conjunctivitis, and small spots with white or bluish-white centers on an erythematous base appearing on the buccal mucosa (Koplik spots). Measles initially infects the respiratory tract and then finds its way into lymph nodes, setting off a chain of events resulting in the typical body rash ~2 weeks after exposure. This red, blotchy (maculopapular) rash usually begins on the face, becomes generalized, and lasts 4–7 days.
Common measles complications include diarrhea (8%), middle ear infection (7%–9%), and pneumonia (1%–6%). Encephalitis, which can result in permanent brain damage, occurs in about 1 per 1,000–2,000 cases of measles. The risk for serious complications or death is highest for children aged ≤5 years, adults aged ≥20 years, and in populations with poor nutritional status or that lack access to health care.
Subacute sclerosing panencephalitis (SSPE) is a progressive neurologic disorder caused by measles virus that usually presents 5–10 years after recovery from the initial primary measles virus infection. SSPE manifests as mental and motor deterioration, which can progress to coma and death. SSPE affects approximately 1 out of every 5,000 measles cases; rates are higher among children <5 years of age.4
Measles Diagnostics
Usually, infection by the measles virus can be diagnosed based on the typical signs and symptoms, especially with the observation of Koplik's spots, and known exposure to an infected person.The CDC and other experts strongly recommend laboratory confirmation. A nasopharyngeal swab, throat swab, or urine specimen, as well as a blood specimen, can be collected from all patients with clinical features indicative of measles. Nasopharyngeal or throat swabs are preferred over urine specimens.5
Like any good medical laboratory professional will tell a healthcare provider or others, the accuracy of any strong laboratory medicine test begins with the accurate collection of the correct specimen. For a measles infection, specimens are acquired from throat, nasal, or urine specimens. A laboratory confirmation can be made via detection of measles IgM antibodies in blood or virus RNA by a reverse transcription polymerase chain reaction (RT-PCR) assay. RT-PCR is particularly useful to confirm inconclusive IgM antibody results.
If blood can’t be utilized, then saliva can also be used for salivary measles-specific IgG or IgA testing. The oral fluid-based IgG or IgA method is not a preferred method, as saliva contains many other fluids and proteins that may make it difficult to collect samples and detect measles antibodies. Also, our antibody repertoire evolves since the time of virus exposure. The antibody IgM is the first type of antibody produced against a newly encountered pathogen, in this case, measles virus. The immune system then refines its own antibodies towards measles, eventually producing high affinity IgG and IgA antibodies. It usually takes approximately 1 week before IgG and IgA appear to a newly encountered virus in the absence of pre-existing immunity. Therefore, salivary IgG and IgA detection methods suffer from sensitivity issues since they are only beginning production after infection.
When testing, it’s always important to consider the geographic regions with low measles prevalence due to high vaccination rates. For example, routine serological methods such as IgM detection may have a reduced positive predictive value and require confirmation by other methods. Direct detection via viral culture (less common) or of viral genomic material using RT-PCR methodologies can play an important role for laboratory confirmation of acute infections. Importantly, genotyping viruses can provide useful molecular epidemiological data for differentiating vaccine from wild-type strains, linking cases and outbreaks, and tracking geographic spread and elimination.6, 7
The Ongoing Outbreak
With the highly contagious nature of the measles virus, additional cases are likely to occur in the outbreak area and the surrounding communities. The Texas Department of State Health Services is working with local health departments to investigate the outbreak.1 The CDC Epidemic Intelligence Service (EIS) is now collaborating on the ground in Texas to assist with the outbreak. The partnership, called Epi-Aid, involves EIS officers who provide on-site support for 1 to 3 weeks to help quickly control health threats while led by local authorities. Of the 198 cases, 80 are unvaccinated, and 113 have an unknown vaccination status. Five patients had received at least one dose of the measles, mumps, and rubella (MMR) vaccine.8
Table 1. Texas Case Count by County
Table 2. Age Ranges of Measles Cases
In neighboring Lea County, New Mexico, the number of measles cases remained at 30, according to the latest update from the New Mexico Department of Health.9 For ongoing, up-to-date information about the outbreak, visit the Texas DSHS Measles Outbreak website. On March 6, 2025, the New Mexico Department of Health confirmed that an unvaccinated adult from Lea County had died from measles.10
As of March 6, 2025, the CDC reports that a total of 222 measles cases were reported by 12 jurisdictions: Alaska, California, Florida, Georgia, Kentucky, New Jersey, New Mexico, New York City, Pennsylvania, Rhode Island, Texas, and Washington.11 There have been 3 outbreaks (defined as 3 or more related cases) reported in 2025, and 93% of cases (207 of 222) are outbreak-associated. For comparison, 16 outbreaks were reported during 2024 and 69% of cases (198 of 285) were outbreak-associated. Of those 222 cases, the vaccine status is reported: Unvaccinated or Unknown: 94%; 1 MMR dose: 4%; and 2 MMR doses: 2%. Approximately 17% (38 of 222) of cases were hospitalized.11
Table 3. Vaccination Status of Confirmed Cases
Vaccination status is classified as unknown when the case investigation is still ongoing or when the person does not know if they were ever vaccinated.
The investigations into the cases who are currently classified as vaccinated are ongoing. A dose of MMR is given to unvaccinated people within 72 hours of their exposure to the measles to lessen the severity of the illness if they get sick from their exposure to the virus. The Texas DSHS is looking into if any of these cases received their MMR dose after exposure.8
Guidance: MMR vaccine and Immunity
The measles, mumps, and rubella vaccine (MMR) is often considered one of the gold standards in immunizations. The efficacy for protection against each of the three diseases is well over 86% after completion of the 2-dose series; specifically for measles, it is ~97% effective. Part of the reason that the vaccine is highly effective against measles is that the virus has adapted and fine-tuned itself to human-to-human transmission since the 10th - 11th century, and antibody and T-cell targets on the virus are fairly evolutionarily stagnant at this point.12 A great contrast to this would be SARS-CoV-2, which has spawned numerous variants since its emergence in 2019 to adapt itself to its new human host. This is the primary reason that COVID-19 vaccines are continuously updated. Another reason that the MMR vaccine has had great success against measles is that humans are the only known host of the virus.12 Contrast that to influenza, which infects birds, pigs, humans, rodents, horses, and others. A broad host range for influenza virus allows it to continuously remodel itself, hence the need for updated vaccines.
For measles, the problem is that not everyone is vaccinated. Since this virus is so contagious, it relies on at least 95% of a community to be vaccinated to prevent a community outbreak. In the US, about 91% of U.S. children ages 19–35 months have been vaccinated.13 However, coverage in some communities like the current west Texas outbreak, is much lower, putting them at greatest risk.
Final Thoughts
Measles was officially eliminated from the United States in 2000, meaning there is no measles spreading within the country, and new cases are only found when someone contracts measles abroad and returns to the country.11 Achieving measles elimination status in the United States was a historic public health achievement.
However, as long as there are pockets of low vaccination coverage throughout the US, we will continue seeing sporadic outbreaks of measles virus. Now, the threat of a large-scale state-wide outbreak in Texas remains low thanks to the relatively high vaccine uptake rates in higher density regions like San Antonio and Austin. Unfortunately, over the past decade or so the public trust in medical and research expertise has eroded due to several complex factors. For example, strong immunization programs undermine themselves: When vaccination rates are high, the disease goes away. As a result, people no longer view the disease as a threat and may choose to not receive a vaccine.
Simply put, the success of vaccination has created, ironically, a public that doesn’t always see the critical importance of continuing the vaccine recommendations by medical experts. The COVID-19 pandemic certainly created societal disruptions, and those impacts will continue to be felt in the misinformation, disinformation, and social media echo chambers that have resulted.
Figure 1. Reported Measles Cases in the U.S. from 1925-2025.11, 14
The burst of measles virus cases in the Texas outbreak is not a surprise to many in public health. It is likely the most contagious human infectious agent known. It is also preventable. For decades, the United States has kept this virus at bay through high vaccination uptake. However, these vaccine uptake rates are not the same across all regions. This can be due to several factors, but the distrust in vaccinations and public health that has been fomented for years is not an innocent party here. The time has long passed for local, state, and federal leaders to address the factors that have led to this preventable outbreak. Old foes will gain ground or re-emerge if we do nothing, but this does not need to happen.15
