CDC tells Americans to CANCEL their flights after finding world's most infectious disease is spreading on planes

The CDC is urging Americans to cancel their upcoming flights if they are not vaccinated against measles.

The agency has upgraded its health travel warning after discovering the virus - one of the most infectious in the world - is spreading on US airplanes.

A previous recommendation that said Americans should 'consider making alternative travel plans' if they could not get vaccinated before departing now says travelers should 'consider postponing their trip.'

Estimates suggest around 10 percent of adults may lack immunity, either due to never receiving the measles, mumps, and rubella (MMR) vaccine or because their immunity has diminished over time — the equivalent of 25million adults.

Measles infections have been detected at the country's biggest airports in recent months amid a resurgence of the virus linked to low vaccination rates.

Now, after investigating dozens of patients who were contagious while flying, the CDC confirmed at least one case where the virus was spread during air travel.

All US travelers are now being recommended to be fully vaccinated for measles before going on any international flights.

And doctors are being advised to give additional measles vaccines to domestic travelers going to Texas, where over 700 people have been infected so far this year.

The CDC's latest update, published Wednesday, reads: 'Travelers can catch measles in many travel settings including travel hubs like airports and train stations, on public transportation like airplanes and trains, at tourist attractions, and at large, crowded events.'

Since the beginning of this year, the CDC has received 62 reports of travelers infected with measles while flying into the US or within the country, a CDC spokesperson told CBS News.

An investigation of 50 of those passengers showed the agency measles spread during air travel in at least one of those situations. The CDC said this is usually based on confirmed infectious individuals sitting next to each other.

The latest airport warning came Friday as three passengers flying into Denver International Airport on the same Turkish Airlines flight tested positive for measles. One of them was a vaccinated adult.

As of 2025, precise data on the number of US adults unvaccinated against measles is limited.

However, historical estimates suggest that approximately 10 percent of adults may lack immunity, either due to never receiving the measles, mumps, and rubella (MMR) vaccine or because their immunity has diminished over time.

Given the US adult population of about 258 million, this could translate to roughly 25 million adults who are potentially unprotected against measles.

Around 90 percent of confirmed cases are tied to outbreaks in the US rather than travel outside the country.

Symptoms - which include a blotchy rash, fever, cough and runny nose - typically develop seven to 21 days after initial exposure.

Measles spreads via airborne droplets released in coughs and sneezes, which can hang in the air for up to two hours after a patient passes.

It is particularly dangerous to young children, with the CDC saying one in 20 unvaccinated children who are infected develop pneumonia while one in 1,000 suffer deadly brain swelling.

A total of 1,088 Americans have been infected so far this year, and two unvaccinated young girls have died.