If you had the chance to ask the director of the U.S. Centers for Disease Control and Prevention what keeps him up at night, you might expect to hear a made-for-Hollywood litany of horrors.
Perhaps a mysterious new virus in the public water system. Or drug-resistant, flesh-eating bacteria sweeping the nation's hospitals. Maybe airline passengers importing Ebola.
Recently, I was among a group from the Association of Health Care Journalists that posed that very question to Dr. Thomas Frieden, during a visit to the institution in Atlanta.
He assured us that he sleeps very well.
"But if you ask what problem could do the most damage," he continued, "it's flu."
Really? Plain old flu?
"It has the ability to spread in a huge way. H1N1 killed over a thousand kids (in the 2009 pandemic)," he said.
If you escaped that one with no more than minor illness or major annoyance at the school closings it prompted, you may not have given it much thought since.
H1N1, popularly known as swine flu, was particularly cruel to the young, who had little natural resistance to a bug that hadn't circulated in decades.
There were many a number of young mothers and babies who died of flu complications. Among them: a 24-year-old Citrus County, Fla., woman who died in September 2009 in her seventh month of pregnancy, leaving behind her husband and toddler.
"It was not a small problem," Frieden told us. "We were lucky. It could have been a lot worse."
But it was bad enough. And the same day Frieden met with us, he announced that this year's flu season has started earlier than in nearly a decade, and shows signs of being severe.
Remember all those warnings to wash your hands, cover your mouth when you sneeze, and stay home when you're sick? That all still holds, but Frieden says his best advice is this -- get a flu shot.
Just about everyone older than 6 months of age should get one, including pregnant women, Frieden said. They're cheap and available without a prescription at pharmacies everywhere.
It takes a couple of weeks for immunity to ramp up after the vaccination, so don't wait to see if others around you get sick.
You may think you're too tough to worry about flu. People often claim they're so healthy they never get flu, or if they do, the symptoms are minor.
But consider this: What if you pick up the virus and pass it along to someone who isn't so tough -- a baby or a pregnant woman, or somebody with diabetes, asthma or another condition that affects immunity?
It really is true that the strong can protect the vulnerable by getting flu shots, according to CDC scientists.
So get that shot.