CDC: All Eligible Persons Should Receive Two MMR Vaccine Shots
Data from a 2025 US Measles Outbreak
A measles outbreak in Colorado in 2025 began with one unvaccinated traveler. It then spread to several people and reached other states. The Centers for Disease Control and Prevention (CDC) recommends that all eligible people receive two doses of the measles, mumps, and rubella (MMR) vaccine.
How the Outbreak Started
The outbreak began when an unvaccinated person traveled through Denver International Airport while infected with measles. The traveler was not a Colorado resident and got measles in the United States before traveling internationally.
While infectious, the person flew into Denver, stayed overnight at a hotel, and then took another flight. Public health officials later linked this exposure to nine new measles cases and one additional case in Colorado. Other states also reported related cases.
Who Got Sick
Of the nine people infected in Colorado, four were among people who had already received two doses of the MMR vaccine.
Those who were vaccinated had milder symptoms than those who were unvaccinated. None of those who had gotten two doses of the MMR vaccine were hospitalized, while three unvaccinated people and one person with unknown vaccination status were hospitalized. All recovered.
Similarly, twice-vaccinated individuals in a large measles outbreak in the Netherlands in 2013-2014 were far less likely to experience severe disease than unvaccinated people. In that outbreak, none of the twice-vaccinated measles cases had complications or were hospitalized, compared with about 14.5% of unvaccinated cases, demonstrating the protective effect of measles vaccination against severe illness.
How Well the MMR Vaccine Works
One dose of the MMR vaccine is about 93% effective at preventing measles. Two doses are about 97% effective.
When vaccinated people do get measles, they have less severe disease and are less likely to need hospital care than people who are not vaccinated.
How Best To Test
In some vaccinated patients, standard nose and throat tests for measles were initially negative. The virus was later found using urine tests.
Because of this, the CDC says that collecting urine samples along with respiratory samples could help doctors find measles cases more easily, especially in vaccinated people.
Measles Is Rising in the United States
This outbreak happened during a year of high measles activity nationwide. In 2025, the United States reported 2,255 measles cases and three deaths. About 11% of patients were hospitalized.
This was the highest number of measles cases reported in the U.S. since 1992.
The CDC’s Message
Measles is very contagious, but it can be prevented. The CDC says the MMR vaccine is the most effective way to protect against measles.
All eligible people should receive the recommended two doses of the MMR vaccine, especially before traveling, to prevent future outbreaks and reduce the spread of measles in the United States.
