WASHINGTON (AP) -- It's flu shot time, and health officials are bracing for a potentially miserable fall and winter.
The clues: The Southern Hemisphere, especially Australia, was hit hard over the past few months with a flu strain that's notorious for causing severe illness, especially in seniors.
And in the U.S., small clusters of that so-called H3N2 flu already are popping up.
"We don't know what's going to happen but there's a chance we could have a season similar to Australia," Dr. Daniel Jernigan, influenza chief at the U.S. Centers for Disease Control and Prevention, told The Associated Press.
The worrisome news came as the government urged Americans Thursday to make sure they get a flu shot before influenza starts spreading widely. Health and Human Services Secretary Tom Price got his own jab to publicize the importance, saying, "There's no reason not to get protected."
Last year, only about 47 percent of the population was vaccinated.
CDC's Jernigan cautions there's no good way to predict how bad the upcoming flu season will be. That H3N2 strain caused infections here last year, too. And although strains that circulate in the Southern Hemisphere often spread to North America and Europe, there's no guarantee it will make a repeat performance.
Still, H3N2 is "the bad actor," said Dr. William Schaffner of Vanderbilt University and the National Foundation for Infectious Diseases. "If you needed another reason to get vaccinated, there it is. Best get that protection."
Also Thursday, World Health Organization flu advisers meeting in Australia recommended updating future vaccines for the Southern Hemisphere to strengthen H3N2 protection.
Flu does constantly evolve, forcing new vaccine to be brewed each year to match the strains specialists expect to cause most illness. In the U.S., CDC's Jernigan said this year's shots aren't perfect -- but that the H3N2 strain traveling around the globe hasn't significantly changed, so the vaccine remains a pretty good match.
"It's the best tool we have right now for preventing disease," he said in an interview.
Some things to know about the once-a-year rite of flu vaccination:
WHO NEEDS A SHOT?
Everybody, starting at 6 months of age, according to the CDC.
Flu is most dangerous for people over age 65, young children, pregnant women and people with certain health conditions such as asthma or heart disease.
But it can kill even the young and otherwise healthy. On average, the CDC says flu kills about 24,000 Americans each year, and last year, the toll included 105 children.
Last year, three-fourths of babies and toddlers -- tots ages 6 months to 2 years -- were vaccinated. So were two-thirds of adults 65 and older.
HOW WELL DOES THE VACCINE PROTECT?
The CDC says people who get flu shots have a 40 percent to 60 percent lower chance of getting seriously ill than the unvaccinated. If someone is infected despite vaccination, generally they have a milder illness than if they'd skipped the shot, Schaffner said.
"I like to tell my patients, 'You're here complaining, that's wonderful -- you didn't die,'" he said.
It takes about two weeks for good protection to kick in. Flu season tends to peak around January, but there's no way to know when it will start spreading widely.
Manufacturers say between 151 million and 166 million doses will be available this year. It's already widely available in doctors' offices and drugstores.
WILL THE SHOT MAKE ME SICK?
You can't get influenza from flu shots, specialists stress. But flu vaccine doesn't protect against colds or other respiratory viruses that people can confuse with influenza.
LOTS OF OPTIONS
The regular flu shot comes in versions that protect against either three or four strains of influenza -- including that problematic H3N2 strain, another Type A strain known as H1N1, and one or two strains of Type B flu.
Ask your doctor or pharmacist about other options which are available for certain age groups.
For needle-phobes, there's a skin-deep vaccine that uses tiny needles, and a needle-free jet injector that shoots another vaccine through the skin.
Two vaccine brands target the 65-and-older crowd. They're especially vulnerable to flu's dangerous complications because they tend to have more underlying health problems than younger people -- and because standard flu shots don't work as well with age-weakened immune systems. One high-dose version contains four times the usual anti-flu ingredient, while a competitor contains an extra immune-boosting compound.
And for those worried about allergies from eggs used in the production process, two more vaccines are egg-free.
SORRY KIDS, NO NASAL SPRAY OPTION
FluMist, a less ouchy nasal spray vaccine, once was popular with children. But last year, a baffled CDC said it was no longer protecting against certain influenza strains as well as regular flu shots -- and told doctors not to use it. That's the same advice this year: Youngsters will need a shot, just like their parents.
And for kids between the ages of 6 months and 8 years who are getting a first-ever flu vaccination, they'll need two doses a month apart.
Insurance covers most flu vaccinations, often without a copayment. For those paying out of pocket, prices can range between $32 and $40.