• The flu can lead to complications like pneumonia, ear infections, and sinus infections. It can also worsen existing conditions, like asthma or diabetes.
• Each year, thousands of people in the U.S. die from the flu and its complications.
• You might hold a baby. Babies under 6 months can't get the flu shot, yet they are way more susceptible to influenza than you are. Plus, infants and toddlers are more likely than adults to be hospitalized or even die from the flu.
• The vaccine may reduce flu illness severity; so while someone who is vaccinated may still get infected, their illness may be milder.
• According to the CDC, in past flu seasons when the match between flu vaccine and circulating strains of flu virus is close, a flu shot is 71 percent effective in reducing flu-related hospitalizations among adults of all ages, and 77 percent effective among adults age 50 and older. The flu shot may reduce a child's risk by 74 percent.

No. The flu vaccine can't give you the flu. But you might develop flu-like symptoms — despite getting a flu shot — for a variety of reasons, including: ·

• Reaction to the vaccine. Some people experience muscle aches and fever for a day or two after receiving a flu shot. This may be a side effect of your body's production of protective antibodies.
• The 2-week window. It takes about two weeks for the flu shot to take full effect. If you're exposed to the influenza virus shortly before or during that time period, you might catch the flu.
• Mismatched flu viruses. In some years, the influenza viruses used for the vaccine don't match the viruses circulating during the flu season. If this occurs, your flu shot will be less effective, but may still offer some protection.
• Other illnesses. Many other diseases, such as the common cold, also produce flu-like symptoms. So you may think you have the flu when you actually don't.

A flu vaccine is needed every season for two reasons. First, the body’s immune response from vaccination declines over time, so an annual vaccine is needed for optimal protection.

Second, because flu viruses are constantly changing, the formulation of the flu vaccine is reviewed each year and sometimes updated to keep up with changing flu viruses. For the best protection, everyone 6 months and older should get vaccinated annually.

Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the viruses that are in the vaccine.