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Is Influenza Contagious?


A viral infectious disease, influenza is contagious and can last three to 14 days if there are no complications.1 Most healthy adults are thought to be infectious and able to shed influenza virus and transmit it others beginning one day before symptoms develop and for five to seven days after becoming ill. It is estimated that some children may be infectious for longer than seven days.2 Severely immunocompromised children and adults may shed influenza virus for weeks or months.3

Both vaccinated and unvaccinated persons can be infected with and shed and transmit influenza virus in respiratory secretions4 and wild-type influenza virus has also been shed and identified in stool.5 Vaccinated and unvaccinated individuals can transmit influenza to others but be asymptomatic and have no apparent clinical symptoms themselves.6 7

Influenza viruses are transmitted through the air by droplets when infected persons cough, sneeze or talk. These droplets can end up in the mouths or noses or inhaled into the lungs of others near a person with influenza.8 Less frequently, a person might also become infected when touching an item or surface with influenza virus on it and then touching their own nose or mouth.9

To avoid transmitting influenza virus – or other types of influenza-like respiratory infections - to others, people who know they are sick should stay home until they are well. Frequent hand washing with soap and water can help prevent the spread of influenza and other viruses. If soap and water is not available, alcohol-based hand sanitizers can also be used. Eating utensils, dishes, linens and other personal items used by those who are sick should not be shared without thorough washing. Surfaces that are frequently touched should be cleaned and disinfected at home, school and work, especially if used by someone who is ill.10

IMPORTANT NOTE:NVIC encourages you to become fully informed about Influenza and the Influenza vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.

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1 CDC. Clinical Signs and Symptoms of Influenza. May 26, 2016.

2 WebMd.com How Long Is the Flu Contagious? Oct. 29, 2017.

3 Pinsky BA, Mix S, Rowe J et al. Long-term Shedding of Influenza A Virus in Stool of Immunocompromised Child. Emerg Infect Dis 2010; 16 (7).

4 Suess T., Remschmidt C, Schink S et al. Comparison of Shedding Characteristics of Seasonal Influenza Virus (Sub) Types and Influenza A (H1N1) pdm09; Germany, 2007-2011. PLOS One 2012; 7(12).

5 Pinsky BA, Mix S, Rowe J et al. Long-term Shedding of Influenza A Virus in Stool of Immunocompromised Child. Emerg Infect Dis 2010; 16 (7).

6 Bouvier NM, Lowen AC. Animal Models for Influenza Virus Pathogenesis and Transmission. Viruses 2010; 2: 1530-1563

7 CDC. How Flu Spreads. Oct. 5, 2017.

8 Bischoff WE, Swett K et al. Exposure to Influenza Virus Aerosols During Routine Patient Care. J Infect Dis 2013; 207(7): 1037-1046.

9 WebMD. How Not to Spread the Flu. Sept. 4, 2016.

10 CDC. How Flu Spreads. Oct. 5, 2017.

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