Influenza (also called 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:
The flu shot is made from an inactivated, killed virus. There are 3 types of flu shots available:
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 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. 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.
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:
Side effects associated with the nasal spray vaccine include:
Certain people should talk to their doctor before receiving the influenza vaccine. These include people who:
The following people should not get the nasal spray:
Good preventive measures include:
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?
Flu—Department of Health and Human Services
Vaccines & Immunizations
Centers for Disease Control and Prevention
Public Health Agency of Canada
Vaccines, Blood & Biologics
US Food and Drug Administration
Fluzone high-dose seasonal influenza vaccine. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/flu/protect/vaccine/qa_fluzone.htm. Updated September 3, 2015. Accessed August 10, 2015.
Immunization schedules. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/vaccines/schedules/index.html. Updated February 7, 2017. Accessed May 22, 2017.
Influenza in adults. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T435301/Influenza-in-adults. Updated September 27,2016. Accessed December 2, 2016.
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 December 2, 2016.
Key facts about seasonal flu vaccine. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/flu/protect/keyfacts.htm. Updated October 22, 2014. Accessed August 10, 2015.
People at high risk of developing flu-related complications. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/flu/about/disease/high_risk.htm. Updated January 8, 2015. Accessed August 10, 2015.
Seasonal influenza vaccine in adults. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T258149/Seasonal-influenza-vaccines-in-adults. Updated September 29, 2016. Accessed December 2, 2016.
Seasonal influenza vaccine in children. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T268332/Seasonal-influenza-vaccines-in-children. Updated September 29, 2016. Accessed December 2, 2016.
10/15/2007 DynaMed Plus Systematic Literature Surveillance http://www.dynamed.com/topics/dmp~AN~T912559/Seasonal-influenza-vaccines-in-the-elderly: Nichol KL, Nordin JD, Nelson DB, Mullooly JP, Hak E. Effectiveness of influenza vaccine in the community-dwelling elderly. N Engl J Med. 2007;357(14):1373-1381.
3/5/2012 DynaMed Plus Systematic Literature Surveillancehttp://www.dynamed.com/topics/dmp~AN~T258149/Seasonal-influenza-vaccines-in-adults: FDA approves first quadrivalent vaccine to prevent seasonal influenza. US Food and Drug Administration website. Available at: http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm294057.htm. Updated March 15, 2012. Accessed August 10, 2015.
Last reviewed September 2016 by David L. Horn, MD, FACP
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.