It's time for flu shots again, and health officials expect to avoid a repeat of the misery last winter, when immunizations weren't a good match for a nasty surprise strain.

More than 170 million doses of flu vaccine are expected this year, with options ranging from traditional shots, a nasal spray, a high-dose version for seniors and even a needle-free injection.

Last year's flu season was especially rough, as a harsh new Type A strain burst on the scene after vaccine doses already were brewed, leaving them less effective than usual. Flu-related hospitalizations of seniors were the highest recorded in the decade that CDC has counted.

This year's vaccine contains protection against that bug and other strains that specialists consider most likely to spread.

Still, flu viruses are tricky, and there's no guarantee another surprise won't crop up.

Fewer than half of Americans get an annual flu immunization, even though the CDC says on average, flu kills about 24,000 people a year in the U.S.

New CDC data shows vaccination rates last year were highest for children ages 6 months to 23 months - at 75 percent, the only age group to meet public health goals. Not far behind were adults over 65 and children ages 2 to 4 - about two-thirds of each group got vaccinated. Least likely to be vaccinated were adults ages 18 to 49.