It’s that time of year again—time to load up on tissues and glare at any sniffling co-workers. Have questions? We have answers. Here’s what you need to know about this season’s hottest commodity: the flu shot.

1. WHAT IS THE FLU, ANYWAY?

“Flu” is short for influenza, which is a nasty disease caused by the influenza virus. The virus affects a person’s lungs, nose, and throat, so symptoms will be concentrated in those areas. The most common symptoms are fever, cough, sore throat, runny nose or stuffy nose, muscle aches, and fatigue. Not everyone will have all of these symptoms. Flu season usually starts in October, peaks in January or February, and ends by May.

2. WHAT'S THE DIFFERENCE BETWEEN THE FLU AND STOMACH FLU?

One is real and one isn't. There's no such thing as stomach flu. The nausea, vomiting, and diarrhea that are commonly called “stomach flu” can be caused by a virus, bacteria, or parasite, but not the influenza virus. Occasionally, the flu virus can cause nausea or vomiting, but this is far more common in children than adults. This may go without saying, but if you’ve been vomiting or have had diarrhea for a few days, it’s time to see a doctor.

3. WHAT'S THE DIFFERENCE BETWEEN SWINE FLU, BIRD FLU, AND REGULAR FLU?

The flu virus comes in many different strains, or types. The strain called H1N1 started in pigs, then spread to humans, and is now a common type of seasonal flu. The bird flu, also known as H5N1 or H7N9, has made a lot of birds sick, but rarely spreads to humans unless they’ve handled infected birds. 

4. WHAT'S IN A FLU SHOT?

Each shot contains a teeny tiny bit of dead flu virus. The virus is grown in fertilized chicken eggs, then extracted and deactivated with microscopic amounts of formaldehyde. A chemical called octylphenol ethoxylate pulls out even smaller pieces of virus, which helps reduce the chances of side effects. Gelatin holds the virus together and keeps it stable during shipping, and a preservative called thimerosol keeps the vaccine from going bad on the shelf. There’s no reason to be concerned about any of these chemicals; they’re present in such small quantities that your body will barely register them. If you have a life-threatening allergy to gelatin or eggs, talk to your doctor before you get your shot. He or she may recommend a different version. (Also, see #9.)

5. I NEVER GET THE FLU. WHY SHOULD I GET A SHOT?

Past performance is not indicative of future results, my friend. Just because you’ve never had it before doesn’t mean you’re invincible. In addition, even if you never have symptoms in your life, you could be carrying the virus around, exposing everyone else to it. And not everybody’s immune system is as robust and macho as yours. Think about babies, and people with compromised immune systems, and pregnant people, and the elderly. Do you really want to be the one who gets them sick?

6. I JUST GOT VACCINATED LAST YEAR. WHY DO I HAVE TO DO IT AGAIN?

There are many, many types of flu. Each year, researchers and public health officials determine which strains seem like they’re going to be a threat, and formulate a vaccine that protects against those strains. To stay protected against the latest flu risks, you must keep your shots up to date.  

7. WHICH TYPES OF FLU DOES THE VACCINE PROTECT AGAINST?

According to the Centers for Disease Control and Prevention, three kinds of flu viruses commonly circulate among people today: influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses. The 2015–2016 flu shot is made to protect against virus strains that are similar to ones we've seen in recent years: an A/California/7/2009 (H1N1)pdm09-like virus; an A/Switzerland/9715293/2013 (H3N2)-like virus; and a B/Phuket/3073/2013-like virus.

Quadrivalent flu shots, which are designed to protect against four types of flu, will protect against an additional B virus.

8. CAN THE FLU SHOT GIVE YOU THE FLU?

No. Your flu shot is either made with dead (deactivated) flu virus or, in the case of the recombinant flu vaccine, with no actual virus at all. You may have some side effects after getting your shot, but those are usually limited to pain or swelling around the site of the injection. In rare cases, you may have a low-grade fever or mild muscle aches, but these are side effects, and not the flu. 

9. CAN I GET A FLU SHOT IF I'M ALLERGIC TO EGGS?

Yes! For a while, doctors were cautioning people with egg allergies to stay away from the flu vaccine, but this seems to have been unnecessary. The American Academy of Allergy, Asthma, and Immunology recently stated that “no special precautions are required for the administration of influenza vaccine to egg-allergic patients, no matter how severe the egg allergy.” If you’re really concerned about an allergic reaction, talk to your doctor. He or she may be able to get you an egg-free flu shot.

10. IF I GET THE FLU, SHOULD I TAKE ANTIBIOTICS?

No! The flu is caused by a virus, not bacteria; antibiotics respond only to bacteria. Antibiotics won’t do anything to fight the flu virus, but they will mess up your body’s bacterial ecosystem and hasten the growth of antibiotic-resistant superbugs. So please don't.