Millions of Americans get seasonal influenza, commonly called the flu, a contagious viral infection that attacks your respiratory system, including the nose, throat and lungs [source: Centers for Disease Control and Prevention].
And the flu is nasty stuff. Each year, more than 200,000 Americans get so sick that they have to be hospitalized, and in a bad flu season, close to 50,000 people may die from flu-related illnesses [source: CDC]. Additionally, the flu costs the U.S. economy more than $10 billion in medical expenses and another $16 billion in lost earnings [source: Trust for America's Health].
So you'd think that by now, we'd all have a pretty good understanding of the flu and what we need to do to deal with it. Well, guess again. Consider, for example, the prudence of getting an annual flu vaccine shot, a tried-and-true method of protecting yourself from the illness that the Centers for Disease Control and Prevention (CDC) now recommends for all Americans ages 6 months and older.
Amazingly, despite that recommendation, fewer than half of Americans go to the trouble of getting the injection, even though it's something that they can do at the local drugstore these days [source: Trust for America's Health].
Why are we so cavalier about our health? One part of the problem, as a 2010 Consumer Reports poll revealed, is that many of us either don't know much about the flu or have the facts dangerously wrong. For example, of the 30 percent of Americans who told pollsters they definitely wouldn't get a flu shot, 41 percent said they worried that flu vaccine was unsafe -- a belief that's been repeatedly refuted by health experts [source: Consumer Reports].
But with the flu, what you don't know can make you sick -- or even dead. To help you to avoid that fate, here are 10 of the most common misconceptions about the flu, along with the real facts.
Anyone who thinks that doesn't know much about history of flu pandemics -- that is, outbreaks of disease that spread around the globe. The dreaded Spanish flu, a particularly vicious strain that emerged in 1918, killed between 20 and 50 million people worldwide, more than the number who died in World War I. Another strain, the Hong Kong flu, killed about 1 million people in 1968-69 [source: Sample].
While the flu's symptoms -- fever, coughing, a painfully sore throat, muscular aches, headaches and extreme fatigue -- are plenty debilitating, most people recover in anywhere from a few days to two weeks [source: CDC]. In severe cases, a flu victim can also get severe dehydration and sepsis -- toxins in the blood that can cause the body's organs to go haywire and begin to fail [source: Sepsis Alliance].
But the real risk may not be from the flu virus's direct effects, but how it weakens the body and makes a person vulnerable to other illnesses, some of which can be fatal. Many seasonal flu-related deaths actually occur a week or two after a person comes down with the flu, when they develop a secondary bacterial infection, such as bacterial pneumonia. In other cases, the flu aggravates an existing chronic illness, such as congestive heart failure or chronic pulmonary heart disease [source: CDC]. People with asthma may experience potentially fatal attacks of that ailment when they come down with the flu [CDC].
It is true that the flu vaccine doesn't always work. According to the CDC, it is effective in preventing a recipient from getting the disease about 60 percent of the time. How well it works depends upon your age and your health; young, healthy people are most likely to get the desired results, according to Dr. Bill Schaeffner, chairman of the preventative medicine department at Vanderbilt University. Another factor is how well this year's vaccine matches to the flu strain that emerges as a threat [source:CNN].
That last part is a continuing challenge for health authorities, because the flu isn't caused by just one virus that remains the same every season. Instead, different strains of the flu continually evolve, and more than one strain may spread simultaneously. That's why each year the vaccine is concocted from three strains of influenza, the ones that researchers guess will probably be the most active, based upon data from previous years [source: Lowrey].
But even if you get a flu shot and still get the flu, your precaution didn't go entirely to waste. The vaccine can help to protect you against some of the disease's harsher complications, experts say [source:CNN].
One important caveat: There are some people who should not get a flu shot without first consulting with their physician. That list includes people who are severely allergic to chicken eggs, those who already have a moderate-to-severe illness with a fever (they should wait to get healthy before getting the vaccine) and those with a history of Guillain-Barre Syndrome, a paralytic illness [source: CDC].
It's amazing how many people seem to be more scared of the vaccine itself than the potentially deadly disease that it's designed to protect against. In fact, a 2012 survey by CVS Pharmacy found that about 35 percent of Americans actually believe that getting vaccinated can give you the flu [source: Weise and Szabo].
That's enough to make medical experts just shake their heads. Injected flu vaccines use what are called "inactivated" vaccines, which essentially have been killed with chemicals. That process leaves just enough proteins in the outer coating of the virus intact that it tricks your immune system into thinking that the virus is a threat. That causes your body to produce white blood cells that are primed to attack any subsequent viral invader that has the same telltale proteins in its coating as the dreaded flu virus. But that crippled microbe itself is incapable of infecting the body and reproducing itself, which is what would make you sick [source: Weise and Szabo].
The FluMist nasal spray vaccine, which is sometimes given to children, does contain a live weakened virus. But the microbe in that vaccine is "cold-adapted," meaning that it's been changed so that it can cause an infection only at the cooler temperatures found in the nose. [source: Weise and Szabo].
That said, the flu vaccine can sometimes cause side effects. These generally range from redness or swelling at the injection site, to headaches and low-grade fevers [source: NFID]. And some people, as we noted in the previous section, shouldn't get flu shots because of certain medical conditions, at least not without consulting their doctors.
Like a lot of misconceptions, this one germinated from a seed of truth -- from a statistical standpoint, you're most likely to come down with the flu in February, several months after the annual flu season actually begins in October or November [source: Brownstein]. And health authorities used to be concerned about the possibility that immunizations would wear off while the flu was still on the march.
But as Dr. James Conway, an associate professor of pediatrics at the University of Wisconsin School of Medicine and Public Health, explained to ABC News in 2008, we now know that isn't so. Instead, the immunity that you gain from the vaccine generally will last from October until the flu season ends in the spring. In some cases, a person's immunity may last for as long as a year [source: Conway].
So, physicians urge everyone to get their flu shots as soon as possible, so that we're protected throughout the entire flu season. But if you don't get a shot early, that's no reason not to go and get one later. It used to be that flu vaccines were only available during a tight time window in October and November, because health authorities felt they had to focus on high-risk groups, such as the elderly, before limited supplies of vaccines ran out. But in recent years, they've greatly expanded immunization efforts, and pharmaceutical companies have ramped up their production of vaccines. Some doctors begin receiving vaccine shipments as early as August [source: Brownstein].
Wrong. As we explained in the previous section, a shot of flu vaccine can give you immunity for many months, and even as long as a year. But that's not forever. According to the Centers for Disease Control and Prevention, there are numerous studies, conducted over different flu seasons and with different types of vaccines and virus strains, which show that the body's immunity does indeed decline over time. And that holds true whether you're inoculated against the virus, or you catch it from somebody who sneezes on you on your morning commuter train [source: CDC].
To make matters worse, there isn't just one type of flu, and flu viruses don't just stay the same, year after year. Instead, these tiny microbes mutate and evolve, just as humans did. But it took complicated organisms like us millions of years to evolve, while viruses, which are much simpler, sometimes do it from one flu season to the next.
They have to in order to survive. Unlike plants, animals and humans, the only way a virus can reproduce itself is by invading a host cell and injecting its genetic material into it. That material then gives the cell instructions to make more copies of the virus, which then spreads to other cells. The host organisms don't go along with this willingly -- their immune systems learn to recognize the distinctive proteins on a particular virus coating and attack it. Thus, in order to overcome that obstacle, viruses continually have to reinvent themselves and become essentially new attackers that your body won't recognize [sources: CBC News, Sepsis Alliance]. That means you have to get annual inoculations to protect against these new threats.
This is a remarkably persistent belief, but there's really no truth to it. The CDC says that the timing of flu outbreaks is unpredictable from year to year, but data show that between the 1982-83 and 2011-12 seasons, the peak month most often has been February, which topped the list in 14 of the years studied, or 47 percent of the time. And the next two months when flu infections most often peak are Jan. and March. December comes in after that, with that month leading the year in infections in only four years, or about 13 percent of the time [source: CDC].
The mind-boggling precision of that bit of data may lead you to wonder: How do public health officials even know that sort of stuff? Government health agencies in both the U.S. and other countries have set up a global system for tracking infectious diseases, including the flu. In the U.S., that work is carried out by the National Respiratory and Enteric Virus Surveillance System, a network of 60 laboratories scattered around the country that test nasal and throat cultures from patients who show up at hospitals and doctors' offices complaining of symptoms. That network works in coordination with an even larger warning system, the U.S. Outpatient Influenza-like Illness Surveillance Network, which includes more than 3,000 healthcare providers in all 50 states. They track all cases of patients with fevers of more than 100 degrees Fahrenheit (38 degrees Celsius) and coughs and/or sore throats [source: CDC].
If you're old enough, you can remember the time when basketball coaches admonished their players to put on their knit caps after taking post-practice showers, and punished anyone who neglected to follow that ritual by making them run laps. But that belief is about as antiquated as black canvas high-top sneakers and socks pulled up to your kneecaps.
As Dr. Donald Denmark, chief medical officer for Tuscon's Carondelet Health Network explained to TV station KVOA in 2013, the notion that you can catch the flu from going out in cold weather, with wet hair or without a coat, or by sitting by a drafty window, is contrary to what we know about how the flu is transmitted. "It's an airborne and droplet transmission, so it's in the presence of someone who sneezes or coughs," Dr. Denmark said. "You inhale the virus that is shed during that contagious period of time."
One reason that people may get mixed up about this is that the peak months for flu infections are in the winter, when it's often cold and wet outside. But medical experts think the reason for increase in illness is that people spend more time indoors, where it's more likely that they'll be exposed to microbes spewed at them from another person's sneezing or coughing [source: Brownstein].
You've probably heard people over the years complain that they're feeling awful and can't keep down solid food because they've come down with something they call the "stomach flu." Unless you have a medical degree, the term makes it easy to confuse that sort of sickness with influenza, but it's really a misnomer. Influenza is a respiratory illness that afflicts the lungs and breathing passages, not the gastrointestinal system. And while vomiting, diarrhea and being sick to your stomach sometimes can be caused by influenza -- usually in kids -- those aren't the main symptoms of the flu, and they're often caused by something else [source: CDC].
So what is the "stomach flu," if it isn't actually influenza? Gastrointestinal discomfort can be caused by a variety of other viruses, bacterial infections and even parasites [source: CDC]. Most often, the stomach flu's unfortunate victims are suffering from some sort of food-borne illness, according to Dr. Tony Brayer, chief medical officer for Sutter Health West Bay Region in California.
But that's scant comfort. Food poisoning, to use the old-fashioned term, is probably just as common as the flu, and it can be just as dangerous. About 48 million Americans are sickened by tainted food each year, with 128,000 of them requiring hospitalization. About 3,000 people die annually from food-borne illnesses. And you can get them at home from food in your refrigerator, just as easily as you can at a greasy-spoon lunch counter or a salad bar without a sneeze guard. Undercooked poultry, meat, unwashed produce and unpasteurized raw milk are common sources [source: Brayer].
If you roam around the Web enough, you're likely to encounter scores of Web sites and bulletin-board posts about the supposed link between vaccines and autism spectrum disorders. Unlike other dubious notions, this one actually stems from something that appeared in a well-respected source.
In 1998, the Lancet, an esteemed British medical journal, published an article in which a researcher claimed that another type of vaccine -- the combined childhood inoculation for measles, rubella and mumps -- was linked to gastrointestinal disease and loss of developmental skills such as language [source: Wakefield et al.]. The article caused a stir, and some parents were reluctant to have their children vaccinated as a result. But according to a 2010 New York Times article, subsequent investigation raised questions about the researcher's ethics and methods, and the Lancet retracted the article. Subsequent studies have failed to show any link between vaccines and autism, the Times reported [source: Harris].
Some autism activists also have raised questions about thimerosal, a preservative containing mercury that has been used in some vaccines and other products since the 1930s. Since the seasonal flu vaccine is produced in large quantities for annual immunization campaigns, some multidose vials contain the preservative to protect against contamination once the containers are opened. According to the CDC, there's no scientific evidence that thimerosal causes any harm to people, except for minor reactions such as redness and swelling at the injection site. But regardless, there's no hazard to children, because only adults get the vaccine containing the preservative. The U.S. Food and Drug Administration eliminated the use of thimerosal in medications given to children back in 2001 [source: CDC].
Don't bother asking your doctor for antibiotics, because they wouldn't help you, and she won't prescribe them anyway. As Dr. Andrew Pavia, a professor of pediatrics and medicine at the University of Utah, explained to ABC News, antibiotic drugs only work against bacteria, and they don't have any effect on viruses such as the ones that cause the flu [source: Pavia].
Where does this misconception come from? If you went to a college infirmary back in the 1970s, you might remember that there was a time when doctors prescribed antibiotics freely for people suffering with flu, colds and other viral illnesses, in an effort to treat bronchitis and other secondary bacterial infections that sometimes occurred. And if you got antibiotics in those days, you actually might have felt a little better afterward. But the antibiotics didn't have anything to do with curing the flu. "If you give people sugar pills or antibiotics, they get better at the same speed," Pavia said.
There are plenty of reasons not to take antibiotics when you don't need them. Their excessive use can make the bacteria in your nose and throat drug-resistant, so that if you do ever get sick from a disease that could be helped by a course of antibiotics, they won't work. Additionally, antibiotics can have some unpleasant side effects, such as rashes and diarrhea, and about one in a thousand people who take them will end up in the emergency room due to such problems [source: Pavia].
There is a medication, Tamiflu, which is designed to reduce the duration of flu symptoms, but according to a 2012 New York Times article, its effectiveness has been a subject of debate [source: Pollack].
Do microbes inside our body have their own circadian rhythms? Learn more about the gut microbiome and circadian rhythms in this HowStuffWorks article.
Author's Note: 10 Misconceptions About the Flu
I was a sickly child who suffered from frequent bouts of bronchitis, which necessitated frequent visits to the doctor's office and lots of shots and bottles of antibiotics. But as an adult, I've mostly been pretty healthy, except for a brief, painful bout with the adult chicken pox in my late thirties. I generally avoid going to the doctor, and I've gone for years without getting a flu shot. After reading the medical literature and the CDC's Web site, though, I now realize that was an ill-advised choice, and that I shouldn't press my luck. In fact, after I finish this article, I'm going to the local pharmacy to get my vaccine shot.
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