Influenza (''flu'') is a contagious disease. It is caused by the influenza virus, which can be spread by coughing, sneezing, or nasal secretions. Other illnesses can have the same symptoms and are often mistaken for influenza. But only an illness caused by the influenza virus is really influenza. Anyone can get influenza, but rates of infection are highest among children. For most people, it lasts only a few days. It can cause: fever, sore throat, chills, fatigue, cough, headache, and muscle aches. Some people get much sicker. Influenza can lead to pneumonia and can be dangerous for people with heart or breathing conditions. It can cause high fever, diarrhea and seizures in children. On average, 226,000 people are hospitalized every year because of influenza and 36,000 die - mostly elderly.
Influenza vaccine can prevent influenza.
Influenza (''flu'') is a contagious disease. It is caused by the influenza virus, which spreads from infected persons to the nose or throat of others. Other illnesses can have the same symptoms and are often mistaken for influenza. But only an illness caused by the influenza virus is really influenza.
There are two types of influenza vaccine:
- Inactivated (killed) vaccine, or the ''flu shot,'' is given by injection into the muscle.
- Live, attenuated (weakened) influenza vaccine is sprayed into the nostrils. This vaccine is described in a separate monograph.
Influenza viruses are always changing. Because of this, influenza vaccines are updated every year, and an annual vaccination is recommended.
Each year scientists try to match the viruses in the vaccine to those most likely to cause flu that year. When there is a close match the vaccine protects most people from serious influenza-related illness. But even when the there is not a close match, the vaccine provides some protection. Influenza vaccine will not prevent ''influenza-like'' illnesses caused by other viruses.
It takes up to 2 weeks for protection to develop after the shot. Protection lasts up to a year.
Some inactivated influenza vaccine contains a preservative called thimerosal. Some people have suggested that thimerosal may be related to developmental problems in children. In 2004 the Institute of Medicine reviewed many studies looking into this theory and concluded that there is no evidence of such a relationship. Thimerosal-free influenza vaccine is available.
People 6 months of age and older can receive inactivated influenza vaccine. It is recommended for anyone who is at risk of complications from influenza or more likely to require medical care:
- All children 6 months and older and all older adults:
- All children from 6 months through 18 years of age.
- Anyone 50 years of age or older.
- Anyone who is at risk of complications from influenza, or more likely to require medical care:
- Women who will be pregnant during influenza season.
- Anyone with long-term health problems with heart disease; kidney disease; liver disease; lung disease; metabolic disease, such as diabetes; asthma; anemia, and other blood disorders.
- Anyone with a weakened immune system due to HIV/AIDS or other diseases affecting the immune system; long-term treatment with drugs such as steroids; cancer treatment with x-rays or drugs.
- Anyone with certain muscle or nerve disorders (such as seizure disorders or cerebral palsy) that can lead to breathing or swallowing problems.
- Anyone 6 months through 18 years of age on long-term aspirin treatment (they could develop Reye Syndrome if they got influenza).
- Residents of nursing homes and other chronic-care facilities.
Anyone who lives with or cares for people at high risk for influenza-related complications:
- Health care providers.
- Household contacts and caregivers of children from birth up to 5 years of age.
- Household contacts and caregivers of people 50 years and older, or anyone with medical conditions that put them at higher risk for severe complications from influenza.
Health care providers may also recommend a yearly influenza vaccination for:
- People who provide essential community services.
- People living in dormitories, correctional facilities, or under other crowded conditions, to prevent outbreaks.
- People at high risk of influenza complications who travel to the Southern hemisphere between April and September, or to the tropics or in organized tourist groups at any time.
Influenza vaccine is also recommended for anyone who wants to reduce the likelihood of becoming ill with influenza or spreading influenza to others.
Plan to get influenza vaccine in October or November if you can. But getting vaccinated in December, or even later, will still be beneficial in most years. You can get the vaccine as soon as it is available, and for as long as illness is occurring in your community. Influenza can occur any time from November through May, but it most often peaks in January or February.
Most people need one dose of influenza vaccine each year. Children younger than 9 years of age getting influenza vaccine for the first time, or who got influenza vaccine for the first time last season but got only one dose, should get 2 doses, at least 4 weeks apart, to be protected.
Influenza vaccine may be given at the same time as other vaccines, including pneumococcal vaccine.
Some people should not get inactivated influenza vaccine or should wait before getting it.
- Tell your doctor if you have any severe (life-threatening) allergies. Allergic reactions to influenza vaccine are rare. Influenza vaccine virus is grown in eggs. People with a severe egg allergy should not get the vaccine. A severe allergy to any vaccine component is also a reason to not get the vaccine. If you have had a severe reaction after a previous dose of influenza vaccine, tell your doctor.
- Tell your doctor if you ever had Guillain-Barré Syndrome (a severe paralytic illness, also called GBS). You may be able to get the vaccine, but your doctor should help you make the decision.
- People who are moderately or severely ill should usually wait until they recover before getting flu vaccine. If you are ill, talk to your doctor or nurse about whether to reschedule the vaccination. People with a mild illness can usually get the vaccine.
A vaccine, like any medicine, could possibly cause serious problems, such as severe allergic reactions. The risk of a vaccine causing serious harm, or death, is extremely small.
Serious problems from influenza vaccine are very rare.The viruses in inactivated influenza vaccine have been killed, so you cannot get influenza from the vaccine.
Mild Problems:
- soreness, redness, or swelling where the shot was given
- fever
- aches
- If these problems occur, they usually begin soon after the shot and last 1-2 days.
Severe Problems:
- Life-threatening allergic reactions from vaccines are very rare. If they do occur, it is within a few minutes to a few hours after the shot.
- In 1976, a certain type of influenza (swine flu) vaccine was associated with Guillain-Barré Syndrome (GBS). Since then, flu vaccines have not been clearly linked to GBS. However, if there is a risk of GBS from current flu vaccines, it would be no more than 1 or 2 cases per million people vaccinated. This is much lower than the risk of severe influenza, which can be prevented by vaccination.
What should I look for?
- Any unusual condition, such as a high fever or behavior changes. Signs of a serious allergic reaction can include difficulty breathing, hoarseness or wheezing, hives, paleness, weakness, a fast heart beat or dizziness.
What should I do?
- Call a doctor, or get the person to a doctor right away.
- Tell your doctor what happened, the date and time it happened, and when the vaccination was given.
- Ask your doctor, nurse, or health department to report the reaction by filing a Vaccine Adverse Event Reporting System (VAERS) form. Or you can file this report through the VAERS web site at http://www.vaers.hhs.gov, or by calling 1-800-822-7967. VAERS does not provide medical advice.
A federal program exists to help pay for the care of anyone who has a serious reaction to a vaccine. For more information about the National Vaccine Injury Compensation Program, call 1-800-338-2382 or visit their website at http://www.hrsa.gov/vaccinecompensation.
- Ask your immunization provider. They can give you the vaccine package insert or suggest other sources of information.
- Call your local or state health department.
- Contact the Centers for Disease Control and Prevention (CDC): call 1-800-232-4636 (1-800-CDC-INFO) or visit CDC’s website at http://www.cdc.gov/flu.
Inactivated Influenza Vaccine Information Statement. U.S. Department of Health and Human Services/Centers for Disease Control and Prevention National Immunization Program. 7/24/2008. 42 U.S.C. section 300aa-26
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