In the Northern hemisphere, winter is the time for flu. In the United States, the flu season can range from November through March, and even past March in some years. During the past 19 flu seasons, months with the heaviest flu activity (peak months) occurred in December in 4 years, January in 5 years, February in 7 years, and March in 3 years (as of 2003).

Influenza (flu) is a highly infectious disease of the lungs, and it can lead to pneumonia. Each year about 114,000 people in the U.S. are hospitalized and about 36,000 people die because of the flu. Most who die are 65 years and older. But children younger than 2 years old are as likely as those over 65 to have to go to the hospital because of the flu.

The vaccine usually protects most people from the flu. Sometimes a person who receives flu vaccine can get the flu, but it will frequently be milder than without the vaccine. Flu vaccine will not protect you from other viruses that sometimes feel like the flu.

The worst side effect you’re likely to get with injectable vaccine is a sore arm. The nasal-spray flu vaccine might cause nasal congestion, runny nose, sore throat, or cough. The risk of allergic reaction to flu vaccine is far less than the risk of severe complications from flu itself.

You might not be able to get this protection if you are allergic to eggs (used in making the injectable vaccine), are very sick with a high fever, or have had a severe reaction to the flu vaccine in the past.

Adults and children with conditions like asthma, diabetes, heart disease, and kidney disease need to get flu vaccine. And people who are active and healthy can also benefit from the protection the flu vaccine offers.

Flu vaccine can be given before or during the flu season. While the best time to get flu vaccine is October or November, getting vaccinated in December or later can still protect you against the flu.

For most people, October and November are considered the best time to vaccinate. October and November might seem "early" in the season, but vaccinating at this time provides the best protection throughout the flu season. This time period for vaccination is recommended because this timing protects most people during the expected periods for peak flu activity.

Recommended timing of vaccination is based on several factors, including observations of flu virus activity in past seasons and overall availability of vaccine. Over nearly 30 years, peaks of flu activity have occurred most often in February. In some years, peak flu activity occurs as early as December. A vaccination in October or November provides protection against flu during both these periods.

Remember, because circulating flu viruses change nearly every year, and because protection provided by the vaccine does wane over the course of a year, one year's vaccine does not protect you during the next season. You need to be vaccinated every year with the vaccine designed to protect you against the viruses circulating that season.

Flu Shots
The flu shot uses an inactivated or “killed” vaccine. This vaccine can’t give you the flu. However, flu vaccine, like other vaccines, can occasionally cause a reaction. Feeling some response to the shot is not unusual. The vaccine acts to stimulate your immune system and prepare you to resist infection. You may feel your body's protective activity through mild symptoms. Also, some people may experience symptoms of mild sickness after getting a flu shot, but these symptoms are not necessarily connected to the shot.

If you do experience a reaction to the flu shot, it is usually local and mild—redness, soreness, and swelling at the site of the injection. Usually if you have this kind of reaction you find that it doesn't interfere with normal daily activity and does not make you feel sick. Fever and more generalized aches and pains can occur but are even less likely; those who are receiving the vaccine for the first time ever are most likely to have this type of reaction. You feel the symptoms, if any, within a few hours of the injection. The symptoms typically cause discomfort, not sickness, and last for a day or two.

Treating a Mild Reaction
To treat a mild reaction to the flu vaccine, use over-the-counter medication only for the symptoms you have (fever, swelling, nasal congestion, cough, and aches and pains). Do not give aspirin to children; use another medication to relieve their fever or aches and pains. If fever is high or symptoms persist or are severe, talk to your doctor or healthcare professional.

Typical influenza (flu) symptoms include fever, body aches, tiredness, cough, and sometimes a sore throat and runny nose. However, these can be symptoms of many diseases, and it can be difficult to tell if you have the flu or another illness by looking at the symptoms alone.

You can be tested for flu. Most of these tests involve having your throat or nose swabbed. This means that the infected area will be wiped with an absorbent material that is then sent to a laboratory for analysis. This type of test is used in the first three to four days of your illness.

Flu tests are not 100 percent accurate. Because the tests are sometimes incorrectly negative or incorrectly positive, they should not be used routinely. Your doctor can determine if you need to be tested for flu; these tests are most useful when a doctor needs the results to help with diagnosis and treatment decisions. For example, if there is an outbreak of a respiratory (breathing) illness, the flu tests can help doctors tell if the illness affecting the population is actually the flu or something else.

For more detailed clinical information about flu tests, please visit the National Center for Infectious Diseases (NCID) website at
http://www.cdc.gov/ncidod/diseases/flu/flu_dx_table.htm