Influenza
What is the Flu?
Influenza (flu) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs. Some people, such as older people, young children, and people with certain health conditions, are at higher risk of serious flu complications. There are two main types of influenza (flu) viruses: Types A and B. The influenza A and B viruses that routinely spread in people (human influenza viruses) are responsible for seasonal flu epidemics each year.
Flu Symptoms
Influenza (flu) can cause mild to severe illness, and at times can lead to death. Flu is different from a cold. Flu usually comes on suddenly. People who have flu often feel some or all of these symptoms:
- fever or feeling feverish/chills
- cough
- sore throat
- runny or stuffy nose
- muscle or body aches
- headaches
- fatigue (tiredness)
- some people may have vomiting and diarrhea, though this is more common in children than adults
How Flu Spreads
People with flu can spread it to others up to about 6 feet away. Most experts think that flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.
When Flu Spreads
People with flu are most contagious in the first three to four days after their illness begins. Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children and some people with weakened immune systems may pass the virus for longer than 7 days.
Symptoms can begin about 2 days (but can range from 1 to 4 days) after the virus enters the body. That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Some people can be infected with a flu virus but have no symptoms. During this time, those people may still spread the virus to others.
Prevention
The best way to reduce your risk from seasonal flu and its potentially serious complications is to get vaccinated every year. Everyone 6 months and older should get a flu vaccine every season with rare exceptions. Vaccination is particularly important for people who are at higher risk of serious complications from influenza. A full listing of people at Higher Risk of Developing Flu-Related Complications is available.
Flu vaccination has important benefits. It can reduce flu illnesses, doctors’ visits, and missed work and school due to flu, as well as prevent flu-related hospitalizations and deaths.
Additional preventative actions to reduce the spread of flu include:- Avoid close contact with people who are sick.
- If you are sick, stay home and limit contact with others as much as possible to keep from infecting them.
- Cover coughs and sneezes.
- Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
- Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub.
- Do not touch your eyes, nose, and mouth. Germs spread this way.
- Clean and disinfect surfaces and objects that may be contaminated with viruses that cause flu.
- For flu, CDC recommends that people stay home for at least 24 hours after their fever is gone except to get medical care or other necessities. Fever should be gone without the need to use a fever-reducing medicine. Note that the stay-at-home guidance for COVID-19 may be different. Learn about some of the similarities and differences between flu and COVID-19.
- In the context of the COVID-19 pandemic, local governments or public health departments may recommend additional precautions be taken in your community. Follow those instructions.
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