Flu season does not officially begin until October. But like holiday merchandise, vaccines are showing up earlier and earlier.

Many pharmacies, supermarkets and big-box discount stores have already hung their "Flu shots today" signs.

Retailers and public health experts peg the preseason vaccination trend to the 2009 H1N1 epidemic, which caught many by surprise. Since then, manufacturers have been releasing their products in August instead of October.

Last year was one of the mildest flu seasons on record, said Dr. Lisa Grohskopf, a medical officer with the Centers for Disease Control and Prevention's (CDC) influenza division. But she says consumers shouldn't get complacent. The CDC still recommends everyone older than 6 months be vaccinated.

"We know the flu is unpredictable, so we can't say what this season will be like," Grohskopf said.

Federal statistics projected that drug manufacturers would make as many as 149 million vaccine doses for this season. The CDC does not anticipate shortages. About 132 million immunizations were given in 2011-12, covering about 45 percent of adults.

The CDC found that in the 2010-11 flu season, about 18 percent of adults received their flu shots in stores, while 40 percent went to doctors' offices.

More people are getting immunized at the same places where they buy their groceries and fill their prescriptions rather than at doctors' offices. Many say they like the convenience. Retailers usually are set up to process insurance billing on-site, so customers with coverage or on Medicare pay nothing out of pocket.

States regulate how vaccines are given outside of medical settings, and the CDC has no recommendations about the best place to get a shot. "We think it's fortunate you now can get a flu vaccine in a wide variety of places," Grohskopf said.

Here are answers to the most commonly asked flu questions.

Q Do I need to be vaccinated against the flu?

A The Centers for Disease Control and Prevention recommends everyone age 6 months and older receive a flu vaccine. Those who most need immunization: seniors age 65 and older, pregnant women, patients with certain medical conditions and caregivers of patients who develop serious complications from contracting the flu.

Q How does a flu shot work?

A Seasonal influenza vaccines combine inactive strains of three flu viruses. The formula, when injected, encourages a person's immune system to build antibodies that fight infection. The vaccine works against the three most commonly circulating flu viruses: influenza B, the H1N1 A strain and the H3N2 A strain.

Q Do I really need a vaccine every year?

A Yes. That's because public health officials annually look at which flu viruses will be most prevalent, then set a vaccine formula designed to thwart those particular strains, which means that the formula can change from year to year. The 2012-13 vaccine cocktail is different from last year's, meaning someone could be unprotected if they skip this year's shot.

Q What about children?

A Children age 6 months through 8 years who never have been immunized for flu will need two shots, four weeks apart. The CDC also is advising that children this age who did not receive at least one dose of the 2010-11 vaccine, or for whom it's not certain they were immunized in 2010-11, should receive two doses of the 2011-12 seasonal vaccine. Ask a doctor for details.

Q When does flu season start?

A It typically begins in October and can last through May, with the season peaking in February. But flu is unpredictable, and seasonal peaks vary by region.

Q Why get vaccinations now instead of later this fall?

A The CDC advises people to be vaccinated as soon as shots are available, so they'll be ready when flu season starts. Many providers began receiving vaccines in August, as manufacturers are shipping earlier. Shots given now should protect you through the season, and you won't have to worry about supply shortages later. It takes your body two weeks following the vaccine to form flu-fighting antibodies. But even if it's past October, the CDC suggests you go ahead and get a shot.

Q I hate needles! Can I take a flu pill instead?

A Sorry, no. But now there is an intradermal vaccine that uses a pin-prick needle, about 90 percent smaller than the standard model. It injects under the skin rather than deep into the muscle, causing less arm-ache afterward. People ages 18 to 64 can have intradermal vaccines.

Q What about the new high-dose shot for seniors?

A The Fluzone High-Dose for people older than 65 first became available in 2010. It has four times the antigen of a standard shot, to boost the immune response, as the body loses the ability to produce antibodies as we age. More side effects have been reported with the high-dose vs. the regular shot. People who have severe egg allergies or who had a serious reaction to a standard flu vaccine should not get the high dose.

Q What about the nasal spray vaccine?

A This vaccine is different from the shots in that it contains a live but weakened version of the flu virus. Healthy people ages 2 to 49 can use the spray. People with egg allergies, and serious medical conditions or weakened immune systems -- and their caregivers -- should not use this vaccine or check with a doctor first.

Q Does Medicare or my insurance cover vaccines?

A Flu shots are covered under Medicare Part B and most private insurance plans. There usually are no out-of-pocket costs to consumers, but ask your provider.

Q What are the risks?

A Serious complications from flu vaccines are rare. Common mild problems include: soreness or redness where the shot was given, fever, headache, fatigue and cough. Allergic reaction symptoms include: difficulty breathing, fast heart rate, dizziness or hives. People with severe allergies, especially to eggs, should talk to their doctor before getting a shot.