The Food and Drug Administration (FDA) has approved vaccines for the 2008-2009 flu season. The flu shot vaccines are designed to protect against strains of flu virus expected to be in circulation this fall and winter. Six manufacturers have begun shipping vaccine for this year’s flu season.

Influenza is a viral infection that sickens millions of people each year and can cause serious complications, especially in children and older adults. Fortunately, the flu vaccine — available in the form of a flu shot or a nasal spray — offers protection against the flu.

Here are the answers to common questions about flu shots.

When is the flu vaccine available?

The flu vaccine is generally offered between September and mid-November, which is typically before the late-fall to early winter start of flu season. However, getting a flu shot even later in the flu season may still protect you. It takes up to two weeks to build immunity following a flu shot.

What kind of protection does the flu vaccine offer?

According to the Centers for Disease Control and Prevention (CDC), when the match between flu vaccine and circulating strains of flu virus is close, a flu shot is between 70 and 90 percent effective in warding off illness in healthy people under age 65. For older adults who don’t live in nursing homes and for people with chronic medical conditions, the flu vaccine is 30 to 70 percent effective in preventing hospitalization for flu or pneumonia. Among nursing home residents, a flu shot is 50 to 60 percent effective in preventing hospitalization and pneumonia, and 80 percent effective in preventing death from influenza.

In some cases, people who get a flu shot can still get the flu, but they may get a much less severe form of the illness and, most important, they’ll have a decreased risk of flu-related complications — especially pneumonia, heart attack, stroke and death — to which older adults are especially vulnerable.

A study published in 2006 showed that the nasal spray flu vaccine (FluMist) was only between 30 and 57 percent effective in preventing the flu in adults. However, another study in 2006 found that giving nasal spray vaccine to school-age children helped reduce the spread of flu in the community. And in 2007, researchers compared the effectiveness of FluMist with the flu shot in children ages 6 months to 5 years. The children treated with FluMist experienced about half as many cases of flu as did those who received the shot. However, FluMist increases the risk of wheezing in this age group — especially in those who already have asthma or recurrent wheezing and in all children under age 2. FluMist is approved for children older than 2 years who don’t have asthma or recurrent wheezing. Consult with your doctor about which form of vaccination may be best for you or your child.

Why do I need to get vaccinated every year?

You need annual flu protection because the influenza virus changes from year to year. The flu vaccine you got last year wasn’t designed to fight the virus strains in circulation this flu season.

Influenza viruses mutate so quickly that they can render one season’s vaccine ineffective by the next season. A CDC advisory committee meets early in the year to estimate which strains of influenza virus will be most prevalent during the upcoming flu season, and manufacturers produce vaccine based on those recommendations.

What are my options for the flu vaccine?

The flu vaccine comes in two forms:

• A shot. A flu shot contains an inactivated vaccine made of killed virus. The shot is usually given in the arm. Because the viruses in the vaccine are killed (inactivated), the shot won’t cause you to get the flu, but it will enable your body to develop the antibodies necessary to ward off influenza viruses. You may have a slight reaction to the shot, such as soreness at the injection site, mild muscle ache or fever. Reactions usually last one to two days and are more likely to occur in children who have never been exposed to the flu virus.
• A nasal spray. Administered through your nose, the nasal spray vaccine (FluMist) consists of a low dose of live, but weakened, flu viruses. The vaccine doesn’t cause the flu, but it does prompt an immune response in your nose and upper airways as well as throughout your body.

What are the main differences between the two types of flu vaccine?

Both the flu shot and the nasal spray help protect you from influenza. But there are differences to consider before deciding between the two.

Who should get the flu vaccine?

Most people who want to reduce the risk of getting influenza can get a flu shot. The CDC recommends the flu vaccine each year if you:

• Are age 6 months up to 19 years
• Are pregnant
• Are 50 years old or older
• Have a chronic medical condition such as asthma, diabetes, or heart, kidney or lung disease
• Have a weakened immune system such as from medications or HIV infection
• Are a resident of a nursing home or other long term care facility
• Are a child care worker or health care worker or live with or care for someone at high risk of complications from the flu

Who shouldn’t get the flu shot?

Don’t get a flu shot if you:

• Have had an allergic reaction to the vaccine in the past.
• Are allergic to chicken eggs.
• Developed Guillain-Barre syndrome, a serious autoimmune disease affecting the nerves outside the brain and spinal cord, within six weeks of receiving the vaccine in the past. People who have experienced Guillain-Barre after the flu vaccine are at higher risk than are others of developing it again.
• Have a fever. Wait until your symptoms improve before getting vaccinated.

Why do children need two doses of the flu vaccine?

Children younger than 9 years old require two doses of the flu vaccine if it’s the first time they’ve been vaccinated for influenza. That’s because children don’t develop an adequate antibody level the first time they get the vaccine. Antibodies help fight the virus if it enters your child’s system. If a flu vaccine shortage was to occur and your child couldn’t get two doses of vaccine, one dose might still offer some protection.

I heard the flu shot isn’t very effective for older adults. Is it worth getting vaccinated if you’re over 65?

If you’re over age 65, the vaccine doesn’t offer as much protection as it would to someone younger because older adults produce fewer antibodies in response to the virus. Still, the vaccine offers more protection than does skipping the shot altogether. More important, the flu vaccine decreases the risk of flu-related complications — especially pneumonia, heart attack, stroke and death — to which older adults are especially vulnerable.

Can I lower my risk of the flu without getting a flu shot?

With or without a flu shot, you can take steps to help protect yourself from the flu and other viruses.

Practice good hygiene
Good hygiene remains your primary defense against contagious illnesses.

• Wash your hands thoroughly and often with soap and water or an alcohol-based sanitizer containing at least 60 percent alcohol.
• Avoid touching your eyes, nose or mouth whenever possible.
• Avoid crowds when the flu is most prevalent in your area.
• Cover your mouth and nose with a tissue when you cough or sneeze.

If I’ve already had the flu, can I get it again?

Once you’ve had the flu, you develop antibodies to the viral strain that caused it. But those antibodies won’t protect you from new or mutated strains of influenza or other viruses.

Is there any medicine to treat the flu?

Antivirals help to prevent the flu or reduce the severity and duration of the illness by a day or two. Antiviral medications are best taken within 48 hours of the onset of your symptoms and are available only by prescription. Ask your doctor about getting a rapid flu test that can verify within a few hours whether you have the flu.

These two antivirals are recommended for treating the flu virus:

• Zanamivir (Relenza)
• Oseltamivir (Tamiflu)

Each of these drugs can cause side effects, including lightheadedness, nausea, loss of appetite and difficulty breathing. They can also lead to the development of antiviral-resistant viruses.

People with the flu, particularly children, who take Tamiflu may be at increased risk of self-injury and confusion. The FDA recommends that individuals with the flu who take Tamiflu be closely monitored for signs of unusual behavior. In July 2007, the FDA approved two lower dose versions of Tamiflu for children. Still, discuss possible side effects with your doctor before starting any antiviral medication.

Your best bet for treating flu symptoms remains the tried and true:

• Rest.
• Get plenty of fluids.
• Take acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin, others) for aches and pains.

It’s also important to eat healthy and get some daily activity to help keep your immune system in top form.