Fall is officially here, and that usually means three things: pumpkin-spiced everything is back in style, our lush trees are about to become leafless sticks, and that sniffle and cough could be your warning that flu season is upon us.

While you've been busy enjoying the summer and taking vacations, drugmakers and researchers around the world have been gearing up by creating vaccines designed to improve your quality of life during the 2017-2018 flu season. But the truth is that misconceptions reign when it comes to understanding the influenza virus, flu vaccines, and flu season in general. Let's look at 12 flu season facts that'll help clear up some common confusion about flu season.

A woman under the blankets with a thermometer in her mouth and a cup of tea.

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1. Up to 65 million American could get the flu over the next year 

In any given year, somewhere between 5% and 20% of the U.S. population comes down with the flu. Based on U.S. Census Bureau population estimates from July 1, 2016, it means that around 65 million people, at the top end of the range, or more than 16 million people at the low end, could deal with the flu over the next year.

2. The flu claims 3,000 to 49,000 lives each year

While the flu is an inconvenience for most people, it can be a life-or-death ailment for those with compromised or undeveloped immune systems, such as the elderly or children. In a given year, influenza will claim between 3,000 and 49,000 lives. When combined with pneumonia, it was the eighth-leading cause of death in the United States in 2016. 

3. $10 billion-plus is spent on treating patients

In addition to being potentially deadly, the flu is also a drag on our healthcare system. Each year, more than $10 billion in spent annually treating patients in hospitals as well as outpatient doctor visits. Flu vaccines are the primary line of defense in keeping folks out of hospitals during flu season. Nevertheless, approximately 200,000 are hospitalized annually with the flu and its related symptoms.

A doctor confidently pondering what he's read on a patient's clipboard.

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4. Flu season never really ends

Though flu season officially begins in October and ends in May, which corresponds with the highest number of recorded cases, people can contract the flu virus at any point during the year. For their part, researchers are unable to concretely pinpoint why the flu spreads so voraciously during the winter months, but some have opined that kids heading back to school provides a perfect arena for quick transmission of the infectious disease. 

5. There are a lot of possible flu virus combinations

According to the Centers for Disease Control and Prevention (CDC), there are four types of influenza virus -- A, B, C, and D -- with D affecting cattle, C responsible for only mild respiratory illnesses, and B and A the primary concern for researchers. Influenza A viruses, which are most often associated with seasonal epidemics, are divided into two subtypes: hemagglutinin (H) and neuraminidase (N). There are 18 different H-subtypes and 11 different N-subtypes, leaving researchers to do some guesswork when developing vaccines.

6. Flu vaccines don't offer foolproof protection from the flu

One of the more common misconceptions about the flu vaccine is that it'll prevent from coming down with the flu. While it is possible that an influenza vaccine could protect you from contracting the flu, that's not its purpose. It's designed to train your immune system how to recognize and attack the flu virus, so as to slow down its spread if you do become infected with the virus. In essence, flu vaccines help to reduce the severity of the flu should you contract it.

A doctor administering a flu vaccine to an elderly patient.

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7. Vaccine effectiveness is between 40% and 60% in most years

The CDC notes that when researchers are spot-on in their efforts to predict which influenza A strains are the likeliest to be present in a flu season, vaccine effectiveness comes in around 40% to 60%. What this suggests is that around half the population that received a vaccine is being kept out of hospitals and doctor's offices each year. The reason the CDC pushes for healthy adults to get their flu shots each year is to ensure they're kept out of hospitals and doctor's offices, so physicians can devote their time to those with weaker immune systems, like the elderly and children.

8. A flu vaccine won't give you the flu

Here it is, the creme de la creme of influenza misconceptions: "If I get a flu shot, I'll get the flu!" Incorrect. All flu vaccines, save for one, are made with inactive strains of the flu virus. Note the emphasis on the word "inactive." These inactive strains are a teaching tool for your immune system, but they can't get you sick. For those of you who choose to use AstraZeneca's (NYSE:AZN) FluMist, it does contain a live attenuated version of the flu virus, but not enough to give you the flu. At worst, you'll wind up with a cold. 

9. FluMist isn't recommended for the upcoming flu season

Sticking with AstraZeneca's FluMist, the CDC has, for a second year in a row, not recommended that physicians or consumers use the nasal spray. Though AstraZeneca's product is probably preferred by children since there's no needle involved, data has shown that its vaccine effectiveness is subpar compared to needle-based vaccine, hence the recommendation by the CDC to use needle-based vaccines. On a constant currency basis, sales of FluMist plunged by just shy of 60% last year for AstraZeneca. 

A biotech lab researcher examining a sample with a microscope.

Image source: Getty Images.

10. Quadrivalent vaccines are the next-generation tool in fighting the flu

As noted, there are a lot of possible influenza A combination types, which makes life difficult on researchers and drugmakers in deciding what type of vaccines should be developed for the upcoming season. There's simply not enough time for drugmakers to wait and see what subtype dominates, and then manufacture that vaccine. That's why they've been turning to quadrivalent vaccines, which are replacing trivalent vaccines. Trivalent vaccines focused on two type A and one type B strain, whereas the quadrivalent vaccines focus on two type A and B strains. Since type B influenza strains dominate toward the end of the flu season, this should provide an added layer of immune protection for consumers.

11. Sanofi's FluZone is the kingpin of all flu vaccines

In terms of dominance, no product is more popular among physicians and consumers come flu season than Sanofi's (NYSE:SNY) FluZone. When lumped in with its other influenza vaccines, Sanofi produced more than $2 billion in sales just from influenza last year.  FluZone has benefited from being offered in a half-dozen dosing options, including one option featuring a needle that's 90% shorter than a traditional needle, which should make kids and needle-phobic adults a lot happier. Until recently, it was also one of the only vaccines approved to treat children as young as six months, but GlaxoSmithKline's (NYSE:GSK) FluLaval quadrivalent vaccine has also been given the green light to treat children as young as six months, too, in the upcoming season. 

12. Only 40% of Americans got a flu shot last year

Last but not least, the CDC reports that just two in five Americans received a flu shot last year. The debate continues over whether it's worth it to get a vaccine, but the vaccine effectiveness data appears to demonstrate that getting the shot can make your flu milder, should you contract it. A higher vaccine use rate is both an opportunity for giants like Sanofi, as well as for the U.S. healthcare system to reduce the costs associated with treating influenza patients.

Sean Williams has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.