Some of the passengers who fell sick on an Emirates flight that landed at John F. Kennedy International Airport on Wednesday probably had the flu or another common respiratory infection, the Centers for Disease Control and Prevention said today based on early test results.

The patients were treated with the flu vaccine and antivirals, reported the CDC in a statement. But the event yesterday started the spread of a different kind of contagion: worry. Today, two more international flights were evaluated by public health officials because people on board were coughing and had sore throats.

“It’s actually pretty common to have somebody coughing in a plane.”

Both of today’s flights were on American Airlines: one from Munich and another from Paris. They landed at Philadelphia International Airport with about a dozen people in total on board who felt sick, according to a statement from the airport. That in itself is not that unusual because of the dry air and the prevalence of cat dander on planes, Allen Parmet, an aerospace medicine expert, told The Verge in an interview yesterday: “It’s actually pretty common to have somebody coughing in a plane.”

But to be safe, “all passengers on the two flights — totaling about 250 plus crew — were held for a medical review and the CDC was notified,” the Philadelphia International Airport said in a statement. No one was running a fever, so they will be released, the CDC said. The people who were sick on the flight should hear back about their test results in 24 hours.

If it turns out to be the flu, this could be an early forecast of the flu season ahead. And the CDC has some tips for keeping the virus from spreading: get vaccinated, and stay home when you’re sick, if you can.