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.