The CDC issued a health advisory Wednesday after flu cases have been rising among young adults.
While flu cases are still low nationally, more than 90% are among children and young adults ages 5 to 24.
The CDC has been investigating an outbreak at the University of Michigan, where hundreds of students have tested positive for the flu. Outbreaks have been reported at other college campuses in the last few weeks.
Experts are now concerned that college students and young adults who have been exposed to the flu could spread it around the country as they travel home for the Thanksgiving holiday.