For the latest information on influenza vaccination, visit the Centers for Disease Control and Prevention website at
the flu) is an upper respiratory infection. It is caused by the influenza virus. Flu strains differ from one year to the next. There are two main kinds that infect humans:
You can get the flu when you breathe in droplets from someone infected with the virus. It can also be spread by touching a contaminated surface and then putting your hand to your mouth or nose.
Each year (usually beginning in October), the flu spreads around the world. Anyone can get it. Some people are at a higher risk of complications. People at higher risk of complications include:
- Being younger than 5 years old
- Being 65 years old and older
Having certain conditions, including:
Chronic lung condition (such as
- Cardiovascular disease
- Kidney or liver disease
- Neurological, blood, or metabolic condition (such as diabetes)
Having a suppressed immune system (such as
- Being pregnant
- Being a child or teen who receives long-term aspirin therapy
- Being American Indian/Alaska Native
- Fever and chills
- Severe muscle aches
- Severe fatigue
- Decreased appetite, other gastrointestinal symptoms (such as nausea, vomiting)
- Runny nose, nasal congestion
- Sore throat
Treatment may include:
- Over-the-counter pain relievers
- Cough suppressants
- Antiviral medicines
The flu shot is made from an inactivated, killed virus. There are three types of flu shots available:
- Regular flu shot (the most common type)—for people aged six months and older, injected into the muscle (usually in the upper arm)
- High-dose shot (Fluzone High-Dose)—for people aged 65 years and older, injected into the muscle
- Intradermal shot (Fluzone Intradermal)—for people aged 18-64 years old, injected into the skin with a smaller needle
There is also a nasal spray (FluMist) made from live, weakened flu viruses. The nasal spray is available for healthy people aged 2-49 years who are not pregnant.
The flu shots and nasal spray contain several influenza viral strains. The type of strains that the vaccine contains change from year to year. The strains are based on which viruses are likely to circulate during that flu season.
The Centers for Disease Control and Prevention (CDC) recommend that anyone aged six months and older should get a flu shot.
It takes about two weeks for the vaccination to protect you against the flu. Even if you have been vaccinated, you can still get the flu. If you have symptoms, tell your doctor.
You can get the flu anytime during the year. But, flu season typically lasts from October to May. The best time to get vaccinated is as soon as the vaccine is available. This will protect you before the flu comes to your community.
Children younger than 9 years old may need two doses of the flu vaccine. This may need to be given to help your child build immunity to the virus. Talk to the doctor to find out how many doses are right for your child.
Almost all people who receive the influenza vaccine have no problems. There are certain risks associated with the vaccine. As with any vaccine, there is a small risk of serious problems, including severe allergic reaction.
Side effects associated with the flu shot include:
- Soreness, redness, and swelling around the injection site
- Low-grade fever
- Muscle aches
Side effects associated with the nasal spray vaccine include:
- Runny nose
- Muscle aches
- Sore throat
Certain people should talk to their doctor before receiving the influenza vaccine. These include people who:
- Have any severe (life-threatening) allergies to chicken eggs
- Have had a severe reaction to the flu vaccine in the past
- Currently are very sick
The following people should not get the
- Are aged 24 months or younger
- Have asthma
- Are aged 2-4 years who have had wheezing in the past 12 months
- Have a condition that may increase their risk of flu complications
- Are aged 50 years and older
- Have a chronic condition (such as heart disease, lung disease, asthma, kidney or liver disease, metabolic disease, blood disorders)
- Have a nerve or muscle disorder
- Have a weakened immune system
- Are in close contact with others who have a weakened immune system
- Have a nasal condition which makes it difficult to breath
- Have gotten any other vaccines in the last 4 weeks
- Pregnant women
- Children or teens on long-term aspirin therapy
Good preventive measures include:
- Avoid close contact with people who have respiratory infections.
- Wash your hands often for 15-20 seconds with soap and water. This is especially important to do when you come in contact with someone who is sick. Rubbing alcohol-based cleaners on your hands is also useful.
- Do not share drinks or personal items.
- Cover your nose and mouth with a tissue when coughing or sneezing.
- Do not put your hands near your eyes, mouth, or nose.
In the event of an outbreak, the primary focus is to vaccinate as many at risk people as possible, especially those in high priority groups. The use of antiviral medications (such as
zanamivir) can reduce the length of the illness when given within two days of onset. Finally, people who are infected should be isolated as much as possible.
WHERE CAN I GET MORE INFORMATION?
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Influenza vaccine in adults. DynaMed website. Available at:
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Influenza vaccine, live, intranasal (2012–2013): What you need to know. Centers for Disease Control and Prevention website. Available at:
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Key facts about seasonal flu vaccine. Centers for Disease Control and Prevention website. Available at:
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Vaccines and immunizations. Centers for Disease Control and Prevention website. Available at:
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8/10/2010 DynaMed's Systematic Literature Surveillance
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3/5/2012 DynaMed's Systematic Literature Surveillance
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9/18/2012 DynaMed's Systematic Literature Surveillance
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Last reviewed March 2013 by Brian Randall, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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