(NBC NEWS) -- Although flu activity is going down in some regions, doctors say it's still important for pregnant women to get their vaccination.
Newborns have protection for the first six months of life if their mothers got the vaccine while pregnant.
"The antibodies cross the placenta, and then if she breast feeds, uh, she's giving more antibodies in the breast milk," explains the March of Dimes' Dr. Edward McCabe.
Dr. McCabe points to a recent study of more than 117,000 pregnancies in Norway.
It concluded the flu shot is safe for pregnant women and their babies without any bad side effects.
Pregnant women who got the flu were more likely to miscarry. That risk was slightly decreased if they'd been vaccinated, but still got a milder or different strain of the flu.
"This serious business. It's important for moms to get their flu shots," Dr. McCabe says.
The flu also tends to hit the oldest members of society hard.
While public health officials say overall flu cases are beginning to decrease, flu-related hospitalization rates among the elderly have risen sharply.
The latest data from the Centers for Disease Control and Prevention show flu cases remain widespread throughout the country.
Only Hawaii, Tennessee and Washington D.C. have been spared the brunt of the viral storm.