Measles Exposures on Transit and at Public Events Raise Travel Safety Questions
The United States is experiencing its most severe measles resurgence in 35 years, with health officials reporting 3,887 confirmed cases as of October 1, 2026 — the highest number since 9,643 cases were documented in 1991. Recent exposures at bars, sports stadiums and on public transportation have prompted questions about travel safety and necessary precautions.
Cases have been reported across 47 jurisdictions, with 42 new outbreaks documented in 2026. Approximately 95% of confirmed cases are outbreak-associated. Pennsylvania, Ohio and New York have recorded the highest case counts in recent weeks, according to the Johns Hopkins Bloomberg School of Public Health U.S. measles tracker.
The Centers for Disease Control and Prevention has confirmed two deaths as of September 28, though the Pennsylvania Department of Health has counted four measles-associated deaths. The CDC notes its death count remains subject to revision as additional information becomes available.
Why Case Numbers May Be Higher
Dr. Paul Offit, director of the Vaccine Education Center at the Children's Hospital of Philadelphia and professor of pediatrics at the Perelman School of Medicine at the University of Pennsylvania, said actual infection rates likely exceed reported figures. Many children, parents or adults may not seek medical care after infection, leading to undercounting of exposures, infections, hospitalizations and deaths.
About 93% of cases in 2026 have occurred among people who are unvaccinated or whose vaccination status is unknown. Only 4% of cases have been among those who received the recommended two doses of MMR vaccine. The majority of cases have been confirmed among children and teenagers aged 19 and younger, with approximately 1 in 10 children under age 5 requiring hospitalization.
Understanding Measles Severity
Dr. Kalyani McCullough, who leads the Vaccine Preventable Disease Epidemiology & Control Section of the Immunizations Branch of the California Department of Public Health, emphasized that measles extends far beyond fever and rash. The disease affects multiple body systems and can have lasting consequences, including immune amnesia — a condition where the measles virus reduces immunity to other infections after recovery.
Among unvaccinated individuals who contract measles, approximately 1 in 5 requires hospitalization. As many as 1 out of every 20 children with measles develops pneumonia. About 1 child out of every 1,000 who contracts measles will develop encephalitis, or brain swelling, which can result in permanent brain damage, deafness or intellectual disability.
How Measles Spreads
Measles ranks among the most contagious diseases known to medicine. It spreads through airborne transmission when an infected person coughs, sneezes or breathes. The virus can remain suspended in the air for up to two hours after an infected person leaves a room, making it possible to contract the disease without direct contact with a sick individual.
The disease has a basic reproduction number of 12 to 18, meaning each infected person can transmit the virus to 12 to 18 other susceptible individuals in a completely susceptible population. Among people who have neither had measles nor been vaccinated, up to 9 out of every 10 exposed will become infected.
Vaccination Remains Primary Protection
Health experts agree that vaccination provides the most effective protection against measles. Two doses of the MMR vaccine are 97% effective at preventing measles infection, while a single dose is 93% effective.
Individuals should verify they have received two MMR vaccine doses, typically administered during childhood. Healthcare providers can review vaccination records and recommend boosters based on individual health history.
Offit stressed that travelers entering the United States from other countries should ensure their vaccinations are current, noting that being unvaccinated in the United States poses significant risk in the current outbreak environment.
Special Considerations for Families
Children typically receive their first MMR dose at approximately 12 months of age. However, McCullough noted that if parents plan international travel with infants or babies aged 6 to 11 months, CDC guidance recommends administering an early vaccine dose.
Immunocompromised individuals who cannot be vaccinated if they have not already received the vaccine may depend on herd immunity — community protection that occurs when a sufficient percentage of the population is vaccinated. For measles, this threshold stands at 95%. Kindergarten vaccination coverage dropped to 92.4% last school year, falling below the protective threshold.
Recent Exposure Incidents
Public health departments have issued exposure notifications following several incidents involving infected travelers. The California Department of Public Health notified residents of potential exposures after an infected and unvaccinated train and bus passenger traveled across the United States and through multiple California counties.
The City of St. Louis Department of Health encouraged residents to monitor for symptoms after an individual who visited local bars and a sports stadium tested positive for measles.
Tracking Challenges
Measles presents tracking difficulties for epidemiologists because symptoms — including fever, cough and rash — typically appear 7 to 14 days after exposure, or as late as 21 days later.
When health officials confirm a measles case, they interview the infected person to identify locations visited and people contacted during the contagious period, typically spanning four days before rash onset through four days after. This eight-day infectious window makes tracking labor-intensive, according to McCullough.
Exposed individuals are generally advised to seek medical guidance and isolate themselves if symptoms develop within three weeks of exposure. Unvaccinated people may be asked to quarantine and may be monitored by public health officials.
Guidance for Travelers
Health experts emphasized that individuals with up-to-date vaccinations and generally good health need not alter travel plans. Roess said vaccinated individuals who maintain regular doctor visits should not be concerned.
For those with concerns, wearing masks in crowded areas provides additional protection. However, vaccination remains the cornerstone of measles prevention, particularly given the virus's ability to spread through the air and persist in spaces after infected individuals have departed.
