People on 4 flights to Texas may have been exposed to measles

A Texas resident with measles may have exposed passengers on four Southwest Airlines flights to the highly contagious virus, officials said.

On August 21 and 22, the individual borrowed Houston Hobby Airport, the Houston Health Service announced on Thursday. The traveler was diagnosed with measles after traveling, a southwestern representative told TIME, but the health department said the person was contagious at the time of the robberies.

Southwest is working with the Centers for Disease Control and Prevention (CDC) to inform passengers on four flights of possible exposure, the airline said. These flights include Flight 5 from Dallas to Houston on August 21; Flight 9, from Houston to Harlingen on August 21st; Flight 665 from Harlingen to Houston on August 22; and Flight 44, from Houston to Dallas, August 22.

The CDC did not immediately respond to TIME's request for comment.

A widespread and effective vaccination has made measles rare in the United States, but 107 cases in 21 states were reported in the first six months of this year alone, in part because of persistent anti-vaccine sentiment.

The viral infection causes symptoms such as rashes, fever, sore throat, inflamed eyes and a runny nose, according to the Mayo Clinic. According to the Houston health service, passengers on the flights concerned could develop symptoms until September 12 and should consult their doctor.

Other travelers who were at the affected airports on August 21 or 22 are at lower risk of infection than those flying with the sick passenger, the health department said.

The alert took a week to include two other high-profile health incidents on the flights. On Wednesday, the passengers and crew of an Emirates flight from Dubai to John F. Kennedy International Airport in New York tested positive for the flu. The next day, 12 passengers on two international flights from American Airlines to Philadelphia had "flu-like symptoms."