The Flu Vaccine

Another way to prevent the flu is by getting a vaccine at the beginning of each flu season (October or November). The earlier you get vaccinated the better, because it takes about two weeks for the vaccine to take its full protective effect. Children under the age of 9 who have never had a flu shot especially need to get an early start, because they will need to have two vaccinations administered about one month apart.

The flu vaccine works by triggering your body's immune system response. When you get a flu vaccine, your body recognizes the flu virus as a foreign invader and produces antibodies to it. The next time your body encounters the flu virus, it will remember that it is a hostile invader and quickly launch an immune attack to kill off the virus.

But if your body remembers the virus, why do you need to get a flu shot every year? First, because flu strains differ from year to year; and second, because immunity declines over time.

The flu vaccine comes in two forms: a shot and a nasal spray.

Photo courtesy U.S. Army U.S. Army soldier receiving the flu vaccine in shot form

The shot, which is normally given in the arm, is made up of three different viruses. The three strains are chosen by scientists working in laboratories around the world. They collect flu viruses and predict which strains will be most prevalent in the coming flu season. The viruses in the shot are inactivated, or dead, which means that they can't actually give you the flu.

The nasal-spray flu vaccine is often referred to as LAIV (Live Attenuated Influenza Vaccine). Unlike the flu shot, it uses a live but weakened version of the virus. Like the shot, it contains three different flu strains. When the LAIV is sprayed into the nose, it works much like the injected form of the vaccine, stimulating the immune system to develop antibodies against the virus.

How effective is the nasal vaccine? One large study found that it reduced the incidence of flu in young children (age 1 to 7) by 92 percent. The study didn't test the effectiveness of the flu spray on adults. Because it is a live vaccine, LAIV is only recommended for healthy people between the ages of 5 and 49.

Who should be vaccinated?

Photo courtesy Simcoe County District Health Unit Flu vaccine vial

Anyone in a high-risk group should be vaccinated at the beginning of every flu season. The CDC recommends that all children, ages 6 to 23 months, get vaccinated. Very young children are more likely to be hospitalized with the flu, and to die from it, than older children and adults. Because infants under 6 months are too young to take the vaccine safely, all people around them (family members and child care workers) should be vaccinated, as well.

Older adults (over age 65) should also be vaccinated, as well as anyone with a chronic health condition like asthma or diabetes. Plus, the CDC recommends that pregnant women and people who work in the healthcare industry be vaccinated.

Who should not be vaccinated?
People who are allergic to chicken eggs should not be vaccinated, because the flu vaccine is grown in eggs and could cause a severe allergic reaction.

Other people who shouldn't receive the flu shot are:

• People who have had a severe reaction to the flu shot in the past
• Anyone who developed Guillain-Barré Syndrome, a rare nerve disease, within six weeks of a previous flu shot
• Infants under 6 months of age
• Anyone who is running a fever

Are there any side effects to the vaccine?
Severe side effects are rare, but many people complain of mild flu-like symptoms, including low-grade fever, muscle aches and tiredness. The side effects usually begin within a few hours after getting the flu shot and can last for about two days.

To find out more about the flu, other diseases and related topics, check out the links on the next page.