Flu Season 2010-11: What to Know to Stay Healthy

To ward off the virus, get a flu shot now. There's no need to miss school or work this flu season.

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Perhaps no flu season in recent memory has been as hyped and harrowing as last year's, when swine flu infected millions and vaccine shortages led to long lines and frustration. As a new flu season dawns, and students head back to school, the latest vaccine—which protects against three strains of flu expected to circulate in months ahead, including the H1N1 virus (aka swine flu)— is already arriving at doctors' offices and other clinics. U.S. News answers pressing questions about the upcoming flu season, the new vaccine, and how to stay healthy.

[H1N1 Not a Threat, But Vaccine Still Warranted]

When does the flu season start and end?

Cases have already been reported by the federal Centers for Disease Control and Prevention. That means flu is striking early this year—the season doesn't officially start until October. Flu activity usually peaks in January, February, and March, and winds down in May, says Henry Bernstein, a professor of pediatrics at Dartmouth Medical School and a member of the American Academy of Pediatrics' infectious diseases committee. What kind of flu season will it be?

Flu is unpredictable, and it's impossible to say with any certainty what kind of season we're in for. "It's an imperfect art," says Harvey Karp, a child development specialist at the University of Southern California School of Medicine." But we went through a pretty robust H1N1 season last year, so a lot of people have immunity to that virus. That should be a good thing this year." Too much stress, however, can lower immunity and increase susceptibility to flu—and continuing economic troubles have us pretty stressed out, he adds. When does the vaccine become available?

It's available now—companies began distributing this year's batch in August. It may arrive later in some towns than others, however. Who should get the flu shot?

For the first time, the CDC is recommending vaccination for everyone 6 months and older—not just the medically vulnerable. Vaccination is particularly important for high-risk groups, including children, those 65 and over, pregnant women, and anyone with an underlying condition that weakens the immune system, such as HIV, asthma, diabetes, or cancer. Since infants 6 months and under can't be vaccinated, their entire family—and their caregivers—should get the shot, Bernstein says. How many shots does this year's vaccine require?

Most people only need one. Children ages 6 months to 9 years, however, need two doses if they've never been vaccinated against flu, or if they only received one dose of the H1N1 vaccine last year. Those doses are given four weeks apart. The first dose primes the immune system, while the second provides immune protection, says Deborah Wexler, a family physician who founded the Immunization Action Coalition, an advocacy group that works to increase immunization rates. If a child needs two doses but only receives one, he or she will have little or no flu protection. Is there a best time to get the flu shot?

There's no advantage to waiting, Bernstein says. The sooner you get it, the sooner you're protected. How long does it take to kick in?

About two weeks. "That's why it's never too late to get vaccinated," Bernstein says. "Some people think that if they didn't get it by November or December, it's too late. That's not true." It's worth getting the shot even toward the end of flu season, because protection develops quickly. Can the vaccine wear off, especially if you get it early?

No. If you get vaccinated now, you'll still be protected when flu season wraps up next year, Bernstein says. [PTA Pushes Flu Shots for Kids]

Should anyone avoid the vaccine?

If you're allergic to chicken eggs, which are used to produce the vaccine, or if you've had a reaction to a past flu vaccine, talk with your doctor first. Signs of a serious reaction include breathing problems, hives, weakness, a fast heartbeat, and dizziness, according to the CDC. If you're sick with a fever, wait to get vaccinated until your symptoms have subsided—that way, you won't confuse symptoms of a reaction with your original sickness, says Carolyn Bridges, associate director for science in the influenza division of the CDC's National Center for Immunization and Respiratory Diseases.

Updated on 8/27/10: The number of flu deaths in this story was updated to reflect the most recent CDC estimates.