By MyHealthNewsDaily Managing Editor
updated 10/26/2012 4:59:15 PM ET 2012-10-26T20:59:15

Flu season is just around the corner, and it typically stretches through the early spring. The Centers for Disease Control and Prevention (CDC) is recommending that everyone older than 6 months get their flu shot.

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During the 2011-2012 flu season, 128 million people in the U.S., or 42 percent of the population, received a flu shot, according to the CDC. That's close to the 43 percent that were vaccinated the previous year.

CDC officials estimated flu vaccinations last year prevented 5 million cases of influenza, and 40,000 hospitalizations.

But myths and misinformation about the flu are circulating like viruses. Here are the facts about the flu vaccine.

Myth: You can get the flu, or a mild case of it, from the flu vaccine.

The flu vaccine injection contains no live virus, only viral proteins, said Dr. Dennis Cunningham, an infectious disease specialist at Nationwide Children's Hospital in Columbus, Ohio.

"It's impossible to get the flu, and it's impossible to spread the flu," from the injection, Cunningham said.

After the injection, some people may experience pain in the arm near the injection site, or develop a low fever — this is a reaction to the vaccine, not a true influenza infection, not even a mild one, he said.

"People with this reaction are able to go to work, that is not the case with the flu. With an influenza infection, you're flat on your back, you're exhausted, hot and hurt," he said.

The flu vaccine that is delivered as a nasal spray, rather than as injection, does contain live viruses, but these viruses have been weakened, and so they also cannot cause the flu, according to the CDC.

Myth: The flu vaccine may not be safe for pregnant women or babies.

The flu vaccine is safe for pregnant women, and for babies older than 6 months, Cunningham said.

In fact, the American Congress of Obstetricians and Gynecologists (the leading group of women's health care physicians) recommends that pregnant women be vaccinated against the flu. "No study to date has shown an adverse consequence of inactivated influenza vaccine in pregnant women or their offspring," according to the ACOG.

The CDC notes that pregnant women should receive the vaccine by injection, not nasal spray.

The flu can be particularly severe for pregnant women, because the body reduces its normal level of immune system function during pregnancy, Cunningham said. For example, during the 2009 H1N1 flu pandemic, pregnant women accounted for a disproportionate number of deaths. This year's flu vaccine includes a strain of the H1N1 virus.

Additionally, the rate of preterm birth among women infected with H1N1 was 30 percent; more than double the usual rate in the U.S. of 13 percent, according to the CDC. Other research has suggested the flu vaccine during pregnancy is linked with a lower risk of stillbirth.

Vaccinated women may also lower their risk infecting their newborns, Cunningham said.

The American Academy of Pediatrics and the CDC recommend that children over 6 months old receive the flu shot. Unvaccinated children have a higher risk of dying from the flu than those are vaccinated, research has shown.  

Myth: Antibiotics can fight the flu if you get it.

Antibiotics only kill bacteria, but the flu is caused by a virus.

There are anti-viral drugs that can fight flu infections, Cunningham said, but they've only been shown to work when they're given with 48 hours of the start of symptoms. "Most people, by the time they go to the doctor, they're past the 48-hour mark," he said.

For patients hospitalized with severe flu, the drugs may help, he said. But they aren't a cure, and for most people who aren't hospitalized, they may only cut down on the duration of the flu by a day or two.

Myth: You don't need to get the flu vaccine if you got it last year — the strains are basically the same.

There are two reasons why it's recommended that people get the flu vaccine every year, Cunningham said.

One reason yearly vaccination is needed is that the strains of the flu virus that are circulating change from year to year. "It's like the common cold — there's more than one type of virus that cause the flu," in fact, there are hundreds of flu viruses, he said.

Each year, health officials identify the viruses that are the most likely to cause illness during the upcoming flu season, according to the CDC.

The vaccine for the 2012-2013 flu season, protects against two type A influenza viruses (one is a strain of the 2009 H1N1 virus, the other is a strain called H3N2), and an influenza B virus.

One of these viruses (the H1N1 virus) was also used to make last year's vaccine, but the H3N2 and B viruses are different from the strains used to make last year's vaccine.

The second reason a flu shot is needed every year is that the immunity that develops after getting the shot wanes by the following year. "If you get your shot in August, you'll be safe though March, but those antibodies won't be for the next flu season," Cunningham said.

Myth: The flu vaccine contains thiomerosal, which may be harmful.

Thiomerosal — a preservative that contains mercury — has never been shown to be harmful, Cunningham said. The type of mercury linked with nervous system damage is methyl mercury, he said. Concerns over methyl mercury levels have led to recommendations that pregnant women avoid eating large amounts of certain types of fish, such as swordfish.

In contrast, thiomerosal is an ethyl mercury compound.

Still, because the preservative raised controversy, especially over a now-disproven link to autism, it was taken out of almost all U.S. vaccines starting in 2001, Cunningham said.

The injectable form flu vaccine is available to health care providers in two ways — they can get large bottles of it, which contain many doses, or they can small bottles, which contain an individual dose of the vaccine.

There is a tiny amount of thiomerosal in the multidose bottles. The preservative ensures that no bacteria will grow in the vaccine, Cunningham said. The individual-dose bottles contain no thiomersal. People concerned about the compounds effects can ask their provider for an individual dose.

The nasal spray form of the flu vaccine contains no thiomerosal, he noted.

Myth: Getting the flu can be a pain, but it's not really a serious disease, so vaccination isn't helpful.

"The flu is certainly a very serious disease," Cunningham said.

Every year, there are typically between 15 million and 60 million cases of the flu reported, Cunningham said. More than 200,000 people with the flu are admitted to hospitals yearly.

Between 3,000 and 50,000 people in the U.S. die of the flu yearly.

One reason people may not perceive the flu as being serious is that cases of the "stomach flu" are mistaken for influenza virus infections.

"True influenza is an infection of the lungs and respiratory tract," Cunningham said. Infected people may develop a high fever, body aches and nasal congestion, he said.

People with the stomach flu — which is commonly caused by a virus called norovirus — have diarrhea, cramping and other gastrointestinal symptoms. Influenza does not cause such symptoms. 

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