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.
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.
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.
Why does this year's vaccine protect against swine flu? I thought the threat was over.
Although H1N1 is no longer considered a pandemic, the virus is still expected to circulate. Flu vaccines are developed with the World Health Organization, which predicts the virus strains that will spread each season. Two other strains, H3N1 and influenza B—are also included in this year's vaccine.
Does being vaccinated mean you won't get the flu or does it just reduce the odds?
The vaccine reduces the likelihood by 70 to 90 percent, according to the CDC. If the flu strains circulating in your community are identical to one of the strains in the vaccine, there will be a very high level of protection. Sometimes, however, the circulating strain and the strain in the vaccine are not a perfect match, meaning protection is not guaranteed, Bernstein says. The vaccine's effectiveness also depends on your age and overall health; those with a weakened immune system, for instance, will still be more susceptible.
Last year we experienced vaccine shortages. Is that likely to happen again this season?
No. About 160 to 165 million doses of the vaccine are expected compared to 114 million doses last year, according to the CDC. "There will be more than enough to go around," Bernstein says.
Is the vaccine ever modified in mid-season to account for new flu strains that arise?
No. The entire production process—predicting which viruses will circulate, producing the vaccine, seeking FDA approval, and packaging and shipping—takes about six months. Once it's been produced, there's no turning back.
How serious a health concern is flu?
Between 5 and 20 percent of people are infected each year, reports the CDC, causing anywhere from 3,300 to 49,000 deaths annually and 200,000 hospitalizations. The flu can also lead to ear infections, sinus infections, and pneumonia. "We should be very worried about it," Bernstein says, "which is why vaccination is so strongly recommended."
How does flu spread?
Mostly through direct contact with droplets in the air like those produced by coughing or sneezing. It circulates easily through airplanes. And touching is another primary culprit, such as when an infected child plays with a toy and then hands it to a friend. "When you rub your eyes or nose and then open a door, you just deposited some virus on the doorknob," Karp says. "Someone coming along 10 minutes later will grab that door, and the virus has spread. Flu is like sticky rice: If you have rice on your hands, I have it on mine, too."
What are the symptoms?
The telltale signs include fever, chills, stomach ache, sore throat, stuffy nose, headache, muscle aches, and fatigue. Even if you don't yet know you're infected, you can transmit flu. "You're contagious for 24 hours before you develop any symptoms," Wexler says.
In addition to the vaccine, what steps can you take to help prevent flu?
Wash your hands frequently, keep your hands off your face, and cover your cough—ideally with a tissue or by coughing into the crook of your arm, rather than your hands, Karp says. In other words, use common sense. Enough sleep is also important, to keep your immune system strong and reduce your chances of catching a bug.
Updated on 8/27/10: The number of flu deaths in this story was updated to reflect the most recent CDC estimates.