Silvana Barbosa, National Center for Health Research
Influenza, also known as the flu, is a very contagious respiratory virus that can cause mild to severe illness. The flu usually comes on suddenly and symptoms include runny or stuffy nose, fever, cough, sore throat, headaches, fatigue, and body aches. Although most people recover quickly, the flu can be fatal, especially for young children, elderly adults, and individuals with a compromised immune system.
The Centers for Disease Control and Prevention (CDC) estimates that from October 1, 2018 to April 6, 2019 there have been 35-40 million cases of the flu in the United States.1
When is the Flu Contagious?
The flu is most contagious during the first three to four days of the illness. However, healthy adults who have contracted the flu can begin to infect others 24 hours before symptoms develop. This means that you may pass the flu to someone else before you even know you are sick. Individuals with the flu are typically contagious for up to 7 days after becoming sick. Children and some people with weakened immune systems may spread the virus to others for more than 7 days.2
Scientists suspect that the flu virus spreads through tiny droplets of fluid that become airborne after coughing, sneezing, or talking. These droplets can then land in the mouths or noses of people nearby. People with the flu can spread the virus to others who are up to 6 feet away. The flu may also spread if a person touches a surface or object (like a doorknob) that has the flu virus on it and then touches their own mouth, nose, or eyes, although this is less likely.3
If you have the flu, stay home and avoid contact with other people unless you are seeking medical help. The U.S. Centers for Disease Control and Prevention (CDC) recommends you stay home for at least 24 hours after your fever is gone without the use of fever-reducing medicines. If you leave home while you are sick, wear a facemask to prevent the spread of the flu and wash your hands often.4
How Long Does the Flu Last?
The flu is typically a short term illness that lasts roughly 3 to 7 days. On average, people who received a flu shot usually experience less severe symptoms for fewer days, but flu vaccines are more effective some years than others.5
People at high risk of developing flu-related complications include individuals with underlying medical conditions, children younger than age 5, adults age 65 and older, pregnant women, and residents of long-term care facilities. These adults and children are more likely to develop complications such as pneumonia, bronchitis, and sinus infections. They may also experience more severe flu symptoms that last longer than 7 days. For a full list of the types of people at highest risk of potential complications, please see here.
Some flu patients are prescribed antiviral medications like Tamiflu. Roche, the company that makes Tamiflu, claims that Tamiflu reduces the number of patients who have serious complications from the flu, such as pneumonia or hospitalization. However, Tamiflu has some serious risks, it only works if taken within 48 hours of infection, and the benefits are not impressive. To learn more, see here.
What Steps Can I Take to Prevent the Flu?
To protect yourself during flu season, avoid close contact with people who might have the flu, stay home when you might have the flu, wash your hands often, and avoid touching your eyes, nose, and mouth.
In addition, the CDC recommends everyone 6 months of age and older get a flu vaccine every season, preferably before the end of October. The seasonal flu vaccine protects against the flu virus strains that experts predicted are likely to be most common during the upcoming season. These predictions are more accurate some years than others. Flu vaccines cause the body to develop antibodies against the virus, to protect against infection. To learn more about the flu vaccine, please click here.
Medical researchers are trying to develop a universal flu vaccine that would eliminate the need to get a flu shot each year and provide protection against newly emerging flu strains, including those that could cause a flu pandemic. On April 3, 2019, the National Institute of Allergy and Infectious Diseases, which is one of the institutes of NIH, announced the first human clinical trial for a universal flu vaccine. The clinical trial will gradually enroll at least 53 adults to test for safety and effectiveness at the NIH clinical center in Bethesda, MD.6
For everything else you need to know about the flu, read here.
All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.
1. 2018-2019 U.S. Flu Season: Preliminary Burden Estimates. (2019). Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/flu/about/burden/preliminary-in-season-estimates.htm. Accessed on April 18, 2019.
2. How Flu Spreads. (2018). Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/flu/about/disease/spread.htm. Accessed on April 18, 2019.
3. How Flu Spreads. (2018). Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/flu/about/disease/spread.htm. Accessed on April 18, 2019.
4. Flu: What To Do If You Get Sick. (2019). Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/flu/treatment/takingcare.htm. Accessed on April 18, 2019.
5. How Long Does the Flu Last? (2018). Harvard Health Publishing. Retrieved from https://www.health.harvard.edu/staying-healthy/how-long-does-the-flu-last. Accessed on April 18, 2019.
6. NIH begins first-in-human trial of a universal influenza vaccine candidate. (2019). National Institutes of Health. Retrieved from https://www.nih.gov/news-events/news-releases/nih-begins-first-human-trial-universal-influenza-vaccine-candidate. Accessed on April 18, 2019.