Why measles is back in the U.S. and what doctors must know now

As measles outbreaks resurface across the U.S., a team of pediatric experts offers urgent clinical and public health insights to prepare a new generation of healthcare providers for a disease many have never encountered firsthand.

State-of-the-Art Review: What’s Old Is New Again: Measles. Image Credit: nobeastsofierce / Shutterstock

Measles is resurging in the United States, mainly due to reduced vaccination rates and increased vaccine hesitancy. This recent surge is challenging clinicians, many of whom have never seen the disease firsthand, with a highly infectious illness once considered eradicated locally.

A team of researchers from the United States has published a State-of-the-Art Review article in the journal Pediatrics to provide an update on measles presentation, clinical course, and outcomes, drawing on the expertise of senior healthcare professionals with extensive experience managing measles cases.

Background

Before the introduction of vaccination, measles was a very common childhood infection worldwide. In the United States, however, it was declared non-endemic in 2000, largely due to the widespread adoption of the measles, mumps, and rubella (MMR) vaccine.

Since measles is a highly contagious virus, with an estimated basic reproduction number (R₀) as high as 18, its widespread transmission can only be prevented by vaccinating more than 95% of people in a community. However, a significant reduction in measles vaccination rates has been observed recently, with 83% of children globally receiving at least one dose of a measles-containing vaccine in 2023, and only 92.7% of American kindergarteners receiving the recommended two MMR doses in the 2023–24 school year.

This decline contributed to a 20% increase in global measles cases between 2022 and 2023. Four outbreaks were reported in the United States in 2023 and 16 in 2024. As of March 25, 2025, three outbreaks had occurred, including a large cluster in Texas with 327 reported cases, 40 hospitalizations, and one death, primarily among unvaccinated individuals.

Clinical presentation

The measles virus has an incubation period of 8–12 days. Children typically develop a prodrome consisting of a brassy cough, conjunctivitis (non-purulent), runny nose, and high fever that lasts 2–4 days. However, the cough may persist for more than 10 days.

Fever can exceed 40°C in uncomplicated cases, typically resolving within two to three days of rash onset.

The classic measles rash appears approximately two weeks after exposure. This macular, morbilliform rash progresses centrifugally, starting at the hairline and behind the ears, spreading downward across the body. The rash usually resolves within a week, often followed by skin peeling.

Koplik spots, tiny white lesions on an erythematous buccal mucosa, may appear early and are considered pathognomonic, though they are often missed due to their short 2–3 day duration.

Diagnosis

According to the Centers for Disease Control and Prevention (CDC), polymerase chain reaction (PCR)-based testing of respiratory samples (preferably nasopharyngeal or throat swabs) is the most effective method for confirming measles.

PCR is most sensitive within three days of rash onset but can detect measles RNA for up to 14 days afterward. Anti-measles IgM testing can aid early diagnosis, though false negatives may occur in the first 72 hours, and false positives are possible in low-incidence settings. Paired IgG antibody testing or follow-up testing is recommended when clinical suspicion remains high.

Measles can mimic other illnesses. Kawasaki disease (KD), for instance, shares features such as rash, conjunctivitis, and fever but lacks the characteristic cough and rash distribution of measles. Laboratory clues such as leukopenia and thrombocytopenia (in measles) versus late-stage thrombocytosis (in KD) may assist in distinguishing the two.

Adenovirus and other viral infections can also resemble measles. Multiplex molecular assays can help differentiate these illnesses.

Given test turnaround delays and limited access to real-time diagnostics, clinicians must maintain a high index of suspicion and initiate infection control based on clinical and epidemiological clues.

Complications

More than half of children with measles develop pulmonary complications, including primary viral pneumonia and secondary bacterial infections, most commonly due to Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. A prolonged fever beyond 2–3 days after rash onset may suggest a superimposed infection.

Other complications include otitis media, diarrhea, myocarditis, pericarditis, appendicitis, thrombocytopenic purpura, and, less frequently, blindness. Measles can also cause profound immune suppression or “immune amnesia,” temporarily erasing immunity to other pathogens.

Encephalitis occurs in up to 1 in 1,000 measles cases, with a 20% mortality rate and long-term neurological deficits in 20–40% of survivors. A delayed but fatal complication, subacute sclerosing panencephalitis (SSPE), may occur years after infection. Previously estimated at 1 in 100,000 cases, its incidence may be as high as 1 in 600 among infants infected before age one.

Immunocompromised children are especially vulnerable, with risks of giant-cell pneumonia and measles inclusion body encephalitis, a complication with a 94% case-fatality rate.

In 2023, measles caused 100,000 deaths globally. The U.S. mortality rate is 1–3 per 1,000 infections, with risks heightened by malnutrition and crowded living conditions.

Treatment

The WHO and AAP recommend age-adjusted vitamin A supplementation for all measles-infected children. Vitamin A reduces the risk of severe complications and is given in two doses: 50,000 IU for infants under 6 months, 100,000 IU for 6–11 months, and 200,000 IU for children over 12 months, with doses administered 24 hours apart.

Bacterial co-infections should be treated with antibiotics targeting likely pathogens. However, routine antimicrobial prophylaxis is not recommended due to insufficient evidence.

For encephalitis, corticosteroids may be used in cases of acute disseminated encephalomyelitis (ADEM), while direct viral CNS involvement is managed supportively. No current treatments have proven effective for halting SSPE progression.

Prevention of viral transmission

Measles patients are infectious from four days before to four days after rash onset. Prompt isolation and infection control are crucial, particularly during outbreaks. Ideally, patients should be placed in airborne infection isolation rooms (AIIRs), though many facilities lack this capacity.

In the 2024 Chicago outbreak, some patients were hospitalized solely for isolation purposes due to a lack of adequate home quarantine facilities, such as in congregate settings.

According to the CDC, individuals are considered immune if they have:

• Laboratory-confirmed measles
• Positive measles-specific IgG
• Documented receipt of two MMR doses after age 12 months

Presumptive immunity based on birth before 1957 is no longer sufficient for healthcare workers during outbreaks.

For individuals over six months of age without documented immunity, post-exposure MMR vaccination is recommended within 72 hours of exposure. Immunoglobulin may be administered to infants under six months, the immunocompromised, and pregnant individuals who cannot receive the live-attenuated vaccine.

Improving vaccine coverage

Sustaining high vaccination coverage is essential to prevent measles resurgence. Vaccine hesitancy, exacerbated during the COVID-19 pandemic, continues to fuel outbreaks.

Evidence-based communication is key. Providers are encouraged to use strong, presumptive statements like “Your child needs MMR today” and to listen empathetically to parental concerns. Highlighting risks such as SSPE and immune amnesia may help underscore the importance of immunization.

Providers should avoid normalizing vaccine refusal, as most parents are willing to vaccinate but may need reassurance and clarity.

Early vaccination (ages 6–11 months) is recommended in outbreak settings or for international travel, though two additional doses are required after 12 months for full protection.

Infants born to mothers with vaccine-derived immunity may not receive adequate transplacental antibodies, making them more susceptible to early measles infection.