WASHINGTON - It's flu vaccine time again - and some lucky shot-seekers will find that the needle has shrunk.

The first flu shot that works with a less-scary skin prick instead of an inch-long needle is hitting the market this fall. Sorry kids, this option so far is just for adults, and it's so brand-new that it will take some searching to find a dose.

But there are plenty of the other varieties - standard shots, a special high-dose shot for seniors and the needle-free squirt-in-the-nose option - to go around. At least 166 million doses of flu vaccine are expected to be produced this year.

The big question is whether people will get it. Usually each year's flu vaccine varies from the previous versions as different influenza strains emerge. This year, the vaccine's a duplicate because the three flu strains that sickened people last winter still are circulating.

Scientific studies aren't clear about how much a person's immunity wanes over a year, although it varies by age and overall health. But federal health officials and the American Academy of Pediatrics weighed the evidence and say don't skip this year's vaccination - it's the only way to be sure your immune system remains revved enough for the best protection.

"You're not going to be able to count on that vaccine protecting you throughout a second season," says Dr. Lisa Grohskopf of the Centers for Disease Control and Prevention.

A yearly vaccination now is recommended for virtually everyone, except babies younger than 6 months and people with severe allergies to the eggs used to make it. Last year, 49 percent of children and 41 percent of adults were vaccinated.

Say you never catch the flu? You could be a carrier, unknowingly spreading the misery when you feel little more than a sniffle, says Dr. William Schaffner of Vanderbilt University, president of the National Foundation for Infectious Diseases.

"You should be vaccinated each and every year to ensure both you're protected and you're giving the maximum protection to people around you," he says.

Here are some questions and answers about flu vaccinations:

Q: How does the new skin-deep vaccine work?

A: Sanofi Pasteur's Fluzone Intradermal uses a needle less than a tenth of an inch long to inject vaccine just below the skin's surface. This layer, called the dermis, is so rich in a certain type of immune cell that the new shot uses a lower dose of the same vaccine that's in regular flu shots. Studies found it triggered as much protection as full-strength muscle shots - although it did cause more skin reactions like redness, swelling and itching. There's little data on pain perception.

But it's only for 18- to 64-year-olds. It hasn't been studied in children's more-tender skin. Sanofi estimates it will sell less than 1 million doses this year while introducing the newly approved product to doctors, before a full market launch next flu season.

Q: What about the original ouchless flu vaccine, the nasal-spray version?

A: MedImmune's FluMist is for a different age group, people ages 2 to 49 who are healthy, meaning no one with underlying health conditions or who is pregnant. Unlike flu shots that are made with killed flu virus, FluMist is made with live but weakened virus.

Q: For older adults, does CDC recommend the high-dose shot?

A: The immune system weakens with age so it doesn't respond as well to an ordinary flu shot. Sanofi's Fluzone High-Dose is a standard into-the-muscle shot but it contains four times the usual dose, to spur more immune response in people 65 and older. First sold last year, studies still are under way to track if that translates into fewer illnesses and hospitalizations. It can cause more of the typical flu-shot side effects. The CDC says it's OK for seniors to choose either a high-dose shot or the regular shots from a variety of manufacturers.

Q: Who's at highest risk from the flu?

A: Young children, anyone 50 or older, anyone with chronic medical conditions such as asthma and certain heart or kidney problems, and pregnant women. A flu vaccination during pregnancy has the added benefit of passing some protection to the baby.

Q: When should I get vaccinated?

A: Anytime, but it takes about two weeks for protection to kick in. Flu typically starts circulating around November, and peaks around January. Some chain pharmacies started vaccinating a month ago. Next month, Hawaii begins offering free in-school vaccinations for elementary and middle school students.

Don't put it off too long, says Dr. Scott Gorenstein of Great Neck, N.Y., an emergency physician whose own son Nate, then 4, nearly died of flu during the 2009 pandemic. The boy already had been exposed by the time vaccine finally was available that fall. Now, Gorenstein says the whole family gets inoculated in early fall - even though Nate has developed a vaccine allergy and as a precaution checks into the hospital for his dose.

"We got lucky," says Gorenstein, who now advises a group called Families Fighting Flu. "You just don't want to be a statistic that is preventable."

Lauran Neergaard covers health and medical issues for The Associated Press.