What Is Flu?
Influenza (in-floo-en-zuh), or flu, is a virus that can spread from person to person. It can cause mild symptoms or can make people feel very sick, causing serious problems that can lead to hospitalization and even death. Even healthy children and adults can get very sick from flu.
Flu spreads mostly through droplets when people cough, sneeze, or talk. Sometimes, it can spread when a person touches something that has the virus on it and then touches their eyes, mouth, or nose. A person can spread flu to others even before they know they are sick and for a week or more after they start to feel sick. People with flu are usually most contagious during the first 3 days of illness.
Burden
While the numbers vary, each year in the US, millions of people get sick from flu, hundreds of thousands are hospitalized, and tens of thousands die from flu and related complications each year. CDC estimates that for the 2023-2024 season, there were at least 34 million illnesses, 380,000 hospitalizations, and 17,000 deaths in the US, including 199 pediatric deaths.
Flu also affects employers and businesses, costing an estimated $11.2 billion in direct and indirect costs in the US annually. Vaccines help prevent millions of cases of respiratory infections each year. During the 2023-2024 respiratory season, CDC estimates that flu vaccination helped prevent at least 7.4 million flu-related illnesses in the US, 3.7 million medical visits, 105,000 hospitalizations, and 3,500 deaths.
Symptoms
Flu is not just a common cold. It usually comes on suddenly, and people with flu may have some or all of the following symptoms (think F.A.C.T.S.):
- Fever
- Aches (muscle, body, and headaches)
- Chills
- Tiredness (fatigue)
- Sudden onset
- Cough, runny or stuffy nose, and/or sore throat
- Vomiting and diarrhea (more common in children than adults)
Prevention
The best way to prevent flu and protect against serious illness is to get a flu vaccine 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 fall, before influenza viruses start spreading in your community, but getting vaccinated any time throughout the season is still beneficial.
Flu vaccines are updated each year to protect against the influenza viruses expected to spread during the upcoming season. Flu vaccines can vary in how well they work, but even when flu vaccination does not prevent infection completely, it can make the illness milder and prevent serious complications. For more than 50 years, hundreds of millions of people in the US have safely received seasonal flu vaccines.
New for 2024-2025
- Updated 2024-2025 flu vaccines will all be trivalent and will protect against 3 types of influenza viruses: H1N1, H3N2, and B/Victoria
- High-dose and adjuvanted inactivated flu vaccines are acceptable options for people age 18-64 years who have had solid organ transplants and take immune-suppressing medication, with no preference over other age-appropriate inactivated or recombinant influenza vaccines
View CDC Flu Vaccination Recommendations for the 2024-2025 US Season
Treatment
Annual flu vaccination is the best way to prevent flu. While antiviral drugs are not a substitute for annual flu vaccination, they can 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 make symptoms milder, shorten the duration of illness by 1-2 days, and prevent serious complications, like pneumonia. Antivirals work best when taken within 48 hours of getting sick, but they can still help if taken later. Healthcare professionals may treat patients based on clinical judgment, local flu activity, and patient conditions.
Learn more about treatment options
Updated September 2024
Source: Centers for Disease Control and Prevention
Key Audiences
Related Resources
Preparing for Respiratory Season
In this recorded webinar, speakers discuss the importance of vaccination to help protect against severe illness during the US respiratory season
2024 National Survey: Attitudes and Behaviors about Influenza, COVID-19, Respiratory Syncytial Virus, and Pneumococcal Disease
2024 national survey on flu, RSV, COVID-19, and pneumococcal disease
Contagious Chronicles: Updated Recommendations for Respiratory Season
In this episode, NFID experts discuss updated recommendations to help protect against COVID-19, influenza (flu), respiratory syncytial virus (RSV), and pneumococcal disease …
Related Posts
Is it Flu, COVID-19, or RSV? How to Tell the Difference
Is it a cold that is causing your cough or runny nose? Or could it be something potentially more serious? Although symptoms can be similar, treatment options may differ …
Help Prevent Flu, COVID-19, and RSV This Season
NFID and CDC experts urge vaccination to help protect against COVID-19, flu, pneumococcal disease, and RSV …
As Concerns about Respiratory Diseases Among Public Drop to New Lows, US Health Officials Urge Vaccination
New NFID survey shows fewer than 1 in 5 US adults are concerned about flu, COVID-19, RSV, or pneumococcal disease, and many do not plan to get vaccinated this fall and winter