NEW YORK, May 31: The CDC is urging unvaccinated Americans to cancel upcoming flights amid rising concerns over measles transmission on airplanes. The agency has upgraded its travel warning after discovering that the highly contagious virus is spreading aboard US flights.

Previously, the CDC advised travelers to "consider making alternative travel plans" if they were unvaccinated. The new guidance now recommends postponing trips altogether until vaccination can be obtained.

An estimated 10 percent of US adults—around 25 million people—may lack immunity to measles, either because they never received the measles, mumps, and rubella (MMR) vaccine or because their immunity has waned over time. Recent measles cases have been reported at major US airports amid a resurgence linked to low vaccination rates.

After investigating dozens of infectious passengers on flights, the CDC confirmed at least one instance of measles transmission during air travel. Consequently, the agency now recommends all US travelers be fully vaccinated before any international trip. Additionally, doctors are encouraged to provide extra measles vaccines to domestic travelers headed to Texas, where more than 700 infections have been reported this year.

In its latest update released Wednesday, the CDC warned that measles can be contracted in various travel settings, including airports, train stations, public transportation, tourist attractions, and crowded events. Since early 2025, the CDC has received 62 reports of measles cases linked to air travel within or into the US. An investigation of 50 infected passengers confirmed at least one case of virus spread on a flight, typically between passengers seated close together.

The latest alert was issued after three passengers on the same Turkish Airlines flight to Denver International Airport tested positive for measles, including one vaccinated adult.

Although precise data on unvaccinated US adults is limited, historical estimates indicate about 10 percent may lack immunity. This figure translates to roughly 25 million adults out of a population of 258 million potentially vulnerable to measles. Most confirmed cases—around 90 percent—are linked to domestic outbreaks rather than infections acquired abroad.

Measles symptoms usually appear 7 to 21 days after exposure and include a blotchy rash, fever, cough, and runny nose. The virus spreads through airborne droplets from coughs and sneezes, which can linger in the air for up to two hours.

Measles poses particular dangers to young children; the CDC reports that one in 20 unvaccinated infected children develop pneumonia, and one in 1,000 suffer fatal brain swelling.

So far in 2025, 1,088 Americans have contracted measles, and two unvaccinated young girls have died.