Far too many young and middle-aged adults still forego the yearly protection, the Centers for Disease Control and Prevention warned.
And this year, Americans have an unprecedented number of vaccine options to choose from: The regular shot; the nasal spray; an egg-free shot for those allergic to eggs; a high-dose shot just for those 65 and older; and a tiny-needle shot for the squeamish. The bigger change: A small number of the regular flu shots, and all of the FluMist nasal vaccine, will protect against four strains of influenza rather than the traditional three.
"There's something for everyone this year," said CDC's Dr. Anne Schuchat.
A severe flu strain swept the country last winter, sparking a scramble for last-minute vaccinations. There's no way to predict if this year will be as bad. But it takes about two weeks for the vaccine to take effect, so health officials say early fall — before flu begins spreading widely — is the best time to start immunizations.
"Now is the time to get vaccinated," said Dr. Paul Biddinger of Massachusetts General Hospital in Boston. "Don't wait until it's in your community."
Boston declared a public health emergency last January when hospitals were filled with flu patients, and Biddinger said he treated many who openly regretted not having been vaccinated.
January and February typically are the peak flu months in the U.S. But small numbers of flu cases circulate for much of the year, and Biddinger said a couple of people have been hospitalized already.
"That first cough or fever is not the time to think about influenza vaccine," Schuchat said.
Flu vaccine is recommended for nearly everyone ages 6 months and older. Yet just 45 percent of the population followed that advice last year. Flu is particularly risky for seniors, children, pregnant women and people of any age with asthma, heart disease and other chronic diseases.
Two-thirds of adults 65 and older were vaccinated last year. So were nearly 57 percent of children, an increase of 13 percentage points over the past two years. The number is even higher among babies and toddlers — 77 percent — and Schuchat said pediatricians get the credit for pushing flu vaccination in recent years.
About half of pregnant women are vaccinated, a number also on the rise since the 2009 flu pandemic illustrated that population's vulnerability.
But only 42 percent of adults younger than 65 were vaccinated, Schuchat said, with rates even lower among 18- to 49-year-olds.
It's not clear why. But "there are no good reasons to skip the influenza vaccine," said Dr. William Schaffner of Vanderbilt University and past president of the National Foundation for Infectious Diseases.
The flu shot cannot give anyone the flu, he stressed. But while it's estimated to cut by about 60 percent the chances of getting the flu, Schaffner said it's "a good vaccine, but it's not a perfect vaccine."
How to choose among the vaccine options, including the new four-strain version? The CDC doesn't recommend one type of flu vaccine over another. All flu vaccine protects against two strains of Type A flu, typically the most severe kind, and one strain of Type B. The new so-called quadrivalent versions protect against two Type B strains.