If you've ever had the flu, you know how bad it can make you feel. You're hot one minute, cold the next, your head aches, and you're completely out of energy. To try to avoid all that misery, some people get a flu vaccine every year.

Who Should Get Vaccinated?

Not everyone needs to get a flu vaccine. Most teens don't need a flu shot because their bodies can handle the infection without developing other problems. But if you have certain medical conditions (like kidney disease, diabetes, HIV, heart problems, or asthma), most doctors recommend that you get a flu shot every year to protect you from complications like pneumonia.

Girls who will be in the second or third trimester of pregnancy during flu season may also need a flu shot. And people who take aspirin regularly for certain medical problems may need a flu shot because they're at risk for developing a serious condition called Reye syndrome if they get the flu.

You might also want to get a flu shot if you live with people who are at risk for health complications if they get the flu, like the elderly and very young children. Ask your doctor about getting a flu shot if you live in the same house as a grandparent or baby (or if you babysit or are in close contact with children younger than 5).

The best time to get a flu shot in the United States is in October or November. This gives the body a chance to build up immunity before the winter flu season. However, you can get a flu shot throughout flu season and still have some protection against the flu. You can also protect yourself against the flu by washing your hands frequently.

What's in a Flu Vaccine?

Flu vaccines are available as a shot or nasal mist (a type of spray that's squirted up the nose). The shot contains killed flu viruses that won't cause people to get the flu, but will cause the body to make antibodies to fight off infection by the live flu virus. Getting a shot of the killed virus causes people to become immune to (protected against) the particular type of live flu virus that's in the vaccine in case they come into contact with it.

The flu shot is about 80% effective against the flu, which means that a few people who get the shot will still get the flu. In addition, the shot only contains certain strains of the virus. If a new flu strain emerges, a person who's had a shot may not be protected against it.

If you hate getting shots but still need to be vaccinated, you may want to ask your doctor about the nasal mist vaccine. The nasal mist is different from the shot because it contains weakened live flu viruses instead of killed viruses. But because it contains live viruses, the nasal mist isn't for everyone. For example, people with weakened immune systems shouldn't get the nasal mist and some things — like steroid use — can affect the immune system. Check with your doctor to see if you can get the nasal mist vaccine — or whether you need a flu vaccine at all.

What About Side Effects?

It's possible to have some minor side effects for 1 or 2 days after getting a flu shot, like soreness in the area where you got the shot. Some people may feel achy or have a mild fever after getting the shot. But the side effects aren't as bad as the flu, which can make some people sick for as long as 2 or 3 weeks.

A few people who get the nasal mist vaccine can develop mild flu-like symptoms that go away after a few days.

The ingredients for flu vaccines are grown inside eggs. So if you're allergic to eggs or egg products, let your doctor know before you get either type of flu vaccine.

Reviewed by: Steven Dowshen, MD
Date reviewed: October 2007