Flu viruses travel through the air in droplets when someone with the infection coughs, sneezes or talks. You can inhale the droplets directly, or you can pick up the germs from an object — such as a telephone or computer keyboard — and then transfer them to your eyes, nose or mouth.
People with the virus are likely contagious from the day before symptoms first appear until five to 10 days after symptoms begin. Children and people with weakened immune systems may be contagious for a slightly longer time.
Influenza viruses are constantly changing, with new strains appearing regularly. If you've had influenza in the past, your body has already made antibodies to fight that particular strain of the virus. If future influenza viruses are similar to those you've encountered before, either by having the disease or by vaccination, those antibodies may prevent infection or lessen its severity.
But antibodies against flu viruses you've encountered in the past can't protect you from new influenza subtypes that are very different immunologically from what you had before. A number of virus subtypes have appeared in humans since the global epidemic (pandemic) of 1918, which killed tens of millions of people.
Oct. 21, 2014
- Labella AM. Influenza. Medical Clinics of North American. 2013;97:621.
- Longo DL, et al. Harrison's Online. 18th ed. New York, N.Y.: The McGraw-Hill Companies; 2012. http://www.accessmedicine.com/resourceTOC.aspx?resourceID=4. Accessed June 19, 2014.
- Dolin R. Epidemiology of influenza. http://www.uptodate.com/home. Accessed June 19, 2014.
- Centers for Disease Control and Prevention, et al. Prevention and control of seasonal influenza with vaccines. Recommendations of the Advisory Committee on Immunization Practices — United States, 2013-2014. MMWR. 2013;62:1. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6207a1.htm?s_cid=rr6207a1_w. Accessed June 15, 2014.
- Zachary KC. Treatment of seasonal influenza in adults. http://www.uptodate.com/home. Accessed June 15, 2014.
- CDC recommendations for influenza antiviral medications remain unchanged. Centers for Disease Control and Prevention. http://www.cdc.gov/media/haveyouheard/stories/Influenza_antiviral2.html. Accessed June 19, 2014.
- Selecting viruses for the seasonal influenza vaccine. Centers for Disease Control and Prevention. http://www.cdc.gov/flu/about/season/vaccine-selection.htm#composition. Accessed June 15, 2014.
- Preventing the flu: Good health habits can help stop germs. Centers for Disease Control and Prevention. http://www.cdc.gov/flu/protect/habits.htm. Accessed June 19, 2014.
You Are ... The Campaign for Mayo Clinic
Mayo Clinic is a not-for-profit organization. Make a difference today.