Skip to content

Cold, Flu, & Cough Health Center

Select An Article

Flu Shot: The Vaccine and Its Side Effects

Font Size

The flu vaccine is the best way to protect yourself from the influenza virus. You should get one every year, unless you have a medical reason not to.

Flu season can begin as early as October and last as late as May. It’s best to get the vaccine as soon as it becomes available each fall.  But you can still get vaccinated in January or later. The flu shot becomes effective about 2 weeks after you get it.

Recommended Related to Cold & Flu

Prevent Flu: Steer Clear of Sick People

You've heard them -- flu-sick sneezers and coughers at the office, day care, shopping mall, or grocery store. Avoiding the flu is no small matter. So what can you do? One sure flu prevention tip is to avoid close contact with people who are sick. Anyone who is at high risk from the seasonal flu -- like young children and older adults -- should avoid crowds and public places during the usual flu season, from late October to mid-March. The honest truth is, in a large environment -- waiting rooms,...

Read the Prevent Flu: Steer Clear of Sick People article > >

Can the Vaccine Give Me the Flu?

No. The viruses in the flu shot are dead. Even the nasal spray, which has a weak version of the flu virus, cannot give you the flu.

What Are the Possible Side Effects?

Most people have no problems from the vaccine.

If you get the flu shot, you might have a mild fever and feel tired or achy after you get vaccinated. Some people also have soreness, redness, or swelling where they got their shot. These problems aren’t serious and don’t last long.

Serious side effects are rare. If they do happen, it's within a few minutes to a few hours after you get the shot. Call your doctor right away if you have trouble breathing, hives, feel weak or dizzy, or have a fast heartbeat afterward.

If you get the nasal spray, you might have side effects like a runny nose, headache, cough, and sore throat. These are milder and shorter than the flu.

Should I Talk to My Doctor Before I Get Vaccinated?

Some people should make sure it’s OK to take the vaccine. Ask your doctor first if:

  • You’ve had an allergic reaction to a flu shot in the past.
  • You’ve had Guillain-Barre syndrome that happened after you got the flu vaccine. That’s a disorder in which the body's immune system attacks part of the nervous system.
  • You’re very ill. If you have a mild illness, it's OK to get vaccinated. Otherwise, talk to your doctor first.

WebMD Medical Reference

Reviewed by Roy Benaroch, MD on July 08, 2015
Next Article:

Today on WebMD

hot toddy
15 tips to help you feel better.
man sneezing into elbow
Do echinacea and vitamin C really help a cold?
teen girl coughing
Get a good night’s rest with these remedies.
elder berry
Eat these to fight colds, flu, and more.
Natural Cold Flu Remedies Slideshow
cold weather
Allergy And Sinus Symptom Evaluator
Boy holding ear
woman receiving vaccine shot
woman with fever
Waking up from sleep
woman with sore throat