Influenza immunization for adults

Influenza (flu) is a viral infection of the throat, bronchial tubes and lungs that occurs most often from November to April. It can cause chills, a moderate to high fever, cough, sore throat, runny nose, headache, muscle aches and tiredness.

Two types of influenza vaccine are now available. The inactivated (killed) influenza vaccine, sometimes called the "flu shot," has been used for many years. As the name implies, the flu shot is given by injection. A live, intranasal influenza vaccine (FluMist, for example) was licensed in 2003. FluMist is an attenuated (weakened) live vaccine sprayed into the nostrils rather than injected into the muscle.


Inactivated vaccine, or flu shot (Fluogen, Flu-shield, Fluzone)
Recommendations
Due to a manufacturing problem, the supply of inactivated flu vaccine for the 2004-2005 season was reduced to about half of what was expected. The Centers for Disease Control and Prevention (CDC) and the Advisory Committee on Immunization Practices (ACIP) initially recommended flu shots for only the following priority groups:

all children ages 6 to 23 months
children ages 6 months to 18 years old on chronic aspirin therapy
people ages 2 to 64 with chronic medical conditions
all women who will be pregnant during flu season
adults age 65 or older
residents of nursing homes and long-term care facilities
health care workers with direct patient care
caregivers and household contacts of children younger than age 6 months
As of January 2005, flu shots were still available in some parts of the United States. Given the supply, the recommendations for flu shots have been expanded to include:

caregivers and household contacts of people in a high-risk group (such as children younger than age 2, people age 65 or older or anyone with a chronic illness)
adults ages 50 to 64
Check with your doctor or county or state health department to see if the vaccine is available in your area.

Other healthy people ages 5 to 49 who aren't pregnant are encouraged to consider the live, intranasal vaccine.

Dose
One shot is given shortly before the flu season.

Effectiveness
When the circulating flu viruses are similar to the virus strains in the vaccine, the flu vaccine is up to 90 percent effective in preventing the flu in healthy adults younger than age 65. It takes one to two weeks for the vaccine to be effective. (The best time to receive the vaccine in the United States is in October or November, although the vaccine is usually available from September to December.) If given too early, immunity may decline before the flu season ends. If given too late, there's a risk of getting the flu before protection begins.

For those who get the flu even after receiving the vaccine, the severity of symptoms and frequency of complications may be reduced.

Side effects
Side effects of the vaccine are usually mild, typically including tenderness, redness or a lump at the injection site, lasting up to two days, beginning six to 48 hours after the vaccination. Less common reactions may include fever, chills, muscle aches or a general feeling of discomfort. An allergic reaction is possible, but rare. (In 1976, the Guillain-Barre syndrome was associated with the flu vaccine. Since then, the condition hasn't been clearly associated with the vaccine. If there's a risk today, it's extremely rare.)

Who should wait to receive the vaccine
Vaccination may be postponed if you have a moderate to severe acute illness.

Who should not receive the vaccine
Vaccination isn't appropriate if you've had a severe allergic reaction to a prior dose of the vaccine or any vaccine component (such as eggs). If you have a history of Guillain-Barre syndrome (GBS), the immunization may not be recommended, especially if you developed GBS within six weeks of having the flu shot.

Pregnancy-specific information
Your doctor may recommend a flu shot if you'll be 14 or more weeks pregnant during the flu season (usually November to March). The vaccine is recommended for any pregnant woman who has any of the high-risk medical conditions listed above.


Live, intranasal influenza vaccine, or nasal spray vaccine (FluMist)
Recommendations
The live, intranasal influenza vaccine may be used by healthy children and adults ages 5 through 49, including household contacts of people at high risk for influenza complications.

Dose
One dose per year is recommended, ideally in October or November. A dose as late as December may still be beneficial, however.

Effectiveness
In one study, the nasal spray vaccine reduced the risk of flu for children by more than 90 percent. In a study among adults, the participants weren't specifically tested for influenza but the Centers for Disease Control and Prevention reported:

19 percent fewer severe respiratory tract illnesses with fever
24 percent fewer mild to moderate respiratory tract illnesses with fever
23 to 27 percent fewer days of illness
13 to 28 percent fewer lost work days
15 to 41 percent fewer clinician visits
43 to 47 percent less use of antibiotics compared with a placebo nasal spray
Side effects
Side effects are usually mild, and may include runny nose, headache, sore throat and cough. An allergic reaction is possible, but rare.

Who should wait to receive the vaccine
Vaccination may be postponed for a moderate to severe acute illness or nasal congestion. (Nasal congestion may limit absorption of the vaccine.)

Who should not receive the vaccine
The nasal spray vaccine isn't appropriate for:

pregnant women
adults age 50 and older
those with chronic heart or lung disease or diseases that weaken the immune system (such as diabetes or kidney failure)
those with a history of Guillain-Barre syndrome
anyone who has a history of allergy to eggs or any vaccine component