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Flu (Influenza)

Influenza (flu) is a highly contagious viral infection of the nose, throat, and lungs that occurs most often in the late fall, winter, and early spring in the US.

Flu can impact people of all ages. It frequently causes people to miss school and work, and in some cases, may cause serious complications such as pneumonia.


Flu is a serious infection that affects between 5-20% of the US population annually. Each year in the US, millions of people get sick, hundreds of thousands are hospitalized, and thousands to tens of thousands die from flu and related complications. Every year flu affects employers and businesses and costs the US approximately $10.4 billion in direct costs for hospitalizations and outpatient visits for adults. During the 2017–2018 flu season, vaccination prevented approximately 7 million flu illnesses, 109,000 flu hospitalizations, and 8,000 flu deaths.


Common symptoms include fever (101-102ºF), muscle/body aches, chills, tiredness, with sudden onset. Other symptoms may include a cough and/or sore throat and a runny or stuffy nose. Fever is less common in people age 65 and older. Diagnostic tests are available to help guide treatment.


The best way to prevent flu is to receive an influenza vaccination every year. The Centers for Disease Control and Prevention (CDC) recommends that everyone age 6 months and older get vaccinated annually. The best time to get vaccinated is in the early fall, before influenza viruses begin spreading in your community. However, vaccination throughout the flu season is still beneficial. To find locations where vaccines are available by zip code, visit

Flu vaccines are updated annually to protect against the influenza strains most likely to circulate each season. Flu vaccine can vary in how well it works, but even in cases when flu vaccination does not prevent infection completely, it can reduce the severity and duration of disease and prevent serious complications. For more than 50 years, hundreds of millions of individuals in the US have safely received seasonal flu vaccines.


Annual flu vaccination is the best way to prevent flu. Antiviral drugs are not a substitute for annual flu vaccination; however, prescription antiviral medications serve as an additional line of defense. CDC recommends that all individuals who are hospitalized, severely ill, or at high risk for developing serious flu-related complications should be treated with antiviral drugs immediately if flu is suspected.

Treatment of flu with antiviral drugs can reduce influenza symptoms, shorten the duration of illness by one to two days, and prevent serious complications, like pneumonia. Antivirals work best when taken within 48 hours of getting sick, but may still be beneficial when given later in the course of illness.

Healthcare professionals may treat patients based on their clinical judgment and knowledge about the level of local flu activity. For additional information, see CDC Influenza Antiviral Medications: Summary for Clinicians.


Featured Resources

Traveling Flu Bug

Traveling Flu Bug

Help #TravelingFluBug spread awareness, not disease! Join the journey to #FightFlu

Additional Resources

Influenza (Flu) Treatment

Certain antiviral drugs can help reduce symptoms of influenza (flu), shorten the duration of illness, and prevent complications

Flu Preparedness Guide

To help prepare for flu season, download the NFID Flu Preparedness Guide to learn more about best practices for treating and preventing the spread of flu, as well as tips on assembling a flu preparedness kit and emergency contact list

Infectious Disease Memes

Share these memes on social media to remind friends and family to #GetVaccinated and stay healthy this holiday season!

More Flu Resources

Flu resources from A to Z from the National Foundation for Infectious Diseases (NFID) and partners

Freddie the Flu Detective

Public service announcement (:30 animated video) on how to detect, prevent, and treat the flu from the National Foundation for Infectious Diseases