‘GMA’ Hot List: What to know about the new flu strain this season Video

Now Playing: CDC reports 20 states experiencing high flu activity

Now Playing: When should you really get the flu shot?

Now Playing: ‘GMA’ Hot List: What to know about the new flu strain this season

Now Playing: White House budget increases spending on HIV research

Now Playing: Spike in cases of dangerous flu strain

Now Playing: Everything you need to know about CBD

Now Playing: Woman born with one arm does intense workouts that are pure inspiration

Now Playing: Later start time for high school students

Now Playing: Spike in injuries for riders using popular sharable electric scooters

Now Playing: How Facebook is fighting anti-vaxxing propaganda

Now Playing: New alert about driving while tired

Now Playing: Kayla Itsines shares her go-to pregnancy workout

Now Playing: Is Sara sleeping on the job?

Now Playing: Can the keto diet cause heart rhythm disorders?

Now Playing: Breast cancer survivor shares cautionary tale of relying solely on thermography

Now Playing: My Morning Routine: Ginger Zee writes what she’s thankful for in the shower

Now Playing: FDA approves nasal spray to treat depression

Now Playing: ‘GMA’ Hot List: Stroke warning signs to know in the wake of Luke Perry’s death

Now Playing: Man possibly cured of HIV: Report

Now Playing: Grandmother crochets more than 2,000 hats for newborns and the results are adorable