U.S. Health Officials say the only thing predictable about the flu is its unpredictability.
Every year, up to 20 percent of Americans come down with the flu. That leads to 200,000 hospitalizations a year, with 20,000 of those hospitalizations being children under the age of 5.
Fox News Medical A Team's Dr. Manny Alvarez says no one is immune to the flu.
"September usually is the season of the flu season and perfect time to get your flu shot in time. So yeah, this is when the reminder begins."
This year's vaccine contains the same strains as last year's, plus two new ones.
More than 170 million doses are expected to be available.
The typical flu season runs from the fall through early spring.