What Is Influenza?
the flu) is an upper respiratory infection. It is caused by a strain of the influenza virus. There are many types of influenza viruses but there are two main kinds that infect humans:
Each year (usually beginning in October), the flu spreads around the world. 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, then putting your hand to your mouth or nose. For most, the flu will cause fever, aches, fatigue, coughing, congestion, loss of appetite, and sore throat. However, some people are more vulnerable to more severe complications which may require hospitalization. Risk factors for severe complications include:
- Age younger than 5 years old or age 65 years and older
Certain medical conditions, including:
Chronic lung condition, such as
asthma or COPD
- Cardiovascular disease
- Kidney or liver disease
- Neurological, blood, or metabolic condition, such as diabetes
Suppressed immune system, such as
those with HIV, cancer, or chronic steroid use
- Current pregnancy
- Long-term aspirin therapy in people under 19 years old
- American Indian and Alaskan Native ancestry
What Is the Influenza Vaccine?
The flu shot is made from an inactivated, killed virus. There are 3 types of flu shots available:
- Regular flu shot (the most common type)—for people aged 6 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
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.
Who Should Get Vaccinated and When?
The Centers for Disease Control and Prevention (CDC) recommend that anyone aged 6 months and older should get a flu shot. Children 6 months to 8 years of age will need 2 doses of the vaccine. This will help your child build immunity to the virus.
It takes about 2 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 (mainly in tropical climates). However in temperate climates, 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.
What Are the Risks Associated With the Influenza Vaccine?
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
Who Should Not Get Vaccinated?
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
- Are currently are very sick with a fever
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
- Have taken influenza antiviral medication within the previous 48 hours
- Pregnant women
- Children or teens on long-term aspirin therapy
What Other Ways Can Influenza Be Prevented?
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.
What Happens in the Event of an Outbreak?
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 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?
Centers for Disease Control and Prevention
Public Health Agency of Canada
US Food & Drug Administration
Fluzone high-dose seasonal influenza vaccine. Centers for Disease Control and Prevention website. Available at:
https://www.cdc.gov/flu/protect/vaccine/qa%5Ffluzone.htm. Updated August 21, 2017. Accessed September 26, 2017.
Immunization schedules. Centers for Disease Control and Prevention website. Available at:
https://www.cdc.gov/vaccines/schedules/index.html. Updated February 6, 2017. Accessed September 26, 2017.
Influenza in adults. EBSCO DynaMed Plus website. Available at:
http://www.dynamed.com/topics/dmp~AN~T435301/Influenza-in-adults. Updated September 11, 2017. Accessed September 26, 2017.
Influenza in children. EBSCO DynaMed Plus website. Available at:
http://www.dynamed.com/topics/dmp~AN~T435305/Influenza-in-children. Updated September 27, 2016. Accessed September 26, 2017.
Key facts about seasonal influenza (flu). Centers for Disease Control and Prevention website. Available at:
https://www.cdc.gov/flu/keyfacts.htm. Updated August 25, 2016. Accessed September 26, 2017.
People at high risk of developing flu-related complications. Centers for Disease Control and Prevention website. Available at:
https://www.cdc.gov/flu/about/disease/high%5Frisk.htm. Updated August 25, 2016. Accessed September 26, 2017.
Seasonal influenza vaccines in adults. EBSCO DynaMed Plus website. Available at:
http://www.dynamed.com/topics/dmp~AN~T258149/Seasonal-influenza-vaccines-in-adults. Updated September 15, 2017. Accessed September 26, 2017.
Seasonal influenza vaccines in children. EBSCO DynaMed Plus website. Available at:
http://www.dynamed.com/topics/dmp~AN~T268332/Seasonal-influenza-vaccines-in-children. Updated September 15, 2017. Accessed September 26, 2017.
Seasonal influenza vaccines in the elderly. EBSCO DynaMed Plus website. Available at:
http://www.dynamed.com/topics/dmp~AN~T912559/Seasonal-influenza-vaccines-in-the-elderly. Updated September 15, 2017. Accessed September 26, 2017.
- Reviewer: EBSCO Medical Review Board
Marcie L. Sidman, MD
- Review Date:
- Update Date: