How Contagious is the Flu?

Dr. James Grant

| 3 min read

James D. Grant, M.D. is senior vice president and chief medical officer at Blue Cross Blue Shield of Michigan. Dr. Grant is a native Michiganian and graduate of Wayne State University School of Medicine. He completed his post graduate training at Northwestern University Medical Center in Chicago. He is a diplomate of the American Board of Anesthesiology, completed his recertification in 2008 and is an associate examiner for the Board.

Influenza is a contagious respiratory virus that can be transmitted all year round. However, in the United States, the incidence of influenza usually rises in the fall, increases in the winter, and greatly decreases again in the spring.
The higher incidence of influenza during the colder months is typically referred to as “flu season,” and the specific timing and severity changes every year depending on which variants are spreading and how.

How does the flu spread to others?

Influenza is usually spread from person to person through tiny droplets emitted when someone coughs, sneezes or talks.
One reason why flu season occurs during the fall and winter months is because people spend more time indoors where these tiny droplets are inhaled by others, or land on items we touch and then touch our eyes, nose or mouth.
Viral particles that are emitted within these droplets can survive for hours or days. If droplets land on a surface and someone touches that surface –a tabletop, doorknob or light switch – and then touches their face, the virus can then be transmitted.

When are people contagious with the flu?

One reason why the flu can spread so quickly is because a person can be contagious before they even realize they have the flu. During the incubation period (the period of time from exposure to when an individual develops symptoms) an individual can spread the flu to others one to two days before they have symptoms. 
People with the flu are most contagious in the first three to four days after their symptoms begin. Once symptoms arise, individuals can still be contagious for up to seven days. Some people, such as those with compromised immune systems, can be contagious for longer.

How to prevent getting the flu and/or potentially spreading to others

While no actions are 100% guaranteed to prevent a person from getting the flu or spreading it, there are several smart practices that greatly reduce the risk:
  1. Get vaccinated – the flu vaccine is the most impactful way to protect yourself and others.
  2. Limit close contact with others, when able.
  3. Cover coughs and sneezes in the elbow or with a tissue; try to avoid using hands.
  4. Practice thorough hand hygiene using either soap and water, or an alcohol-based hand sanitizer.
  5. Stay home if experiencing flu-like symptoms like fever, cough, sore throat, runny nose, chills, etc.
  6. Wear a mask, especially around people more susceptible (infants, elderly, immunocompromised).
  7. Avoid touching the face including eyes, nose, mouth and ears. These are all “points of entry” for the flu virus.
  8. Clean and disinfect surfaces often – particularly “high touch” surfaces such as counter tops, doorknobs, light switches, keypads, touchscreens, remote controls and faucet handles.
There are many ways to prevent getting or spreading the flu. Individuals should consult with their physician about whether and what type of flu vaccine is appropriate for them.
James D. Grant, M.D., is senior vice president and chief medical officer at Blue Cross Blue Shield of Michigan. For more health tips and information, visit MIBluesPerspectives.com. 
Photo credit: Getty Images
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