Flu (Influenza): Overview

"What is the flu?"

The flu is a contagious viral infection of the respiratory system that is caused by the influenza virus. Symptoms cause by the virus can range from mild to severe. Most people will recover from the flu within a matter of a few days to just under two weeks. However, some can develop complications that can result in hospitalization or even death. The best way to prevent the flu is by getting a flu vaccination. 


People who have the flu often feel some or all of the following symptoms: 

  • Fatigue (very tired) 
  • Muscle or body aches 
  • Cough 
  • Headaches 
  • Sore throat 
  • Fever 
  • Runny or stuffy nose 
  • Vomiting and diarrhea (more common in children) 

How is it spread? 

The flu is primarily spread from person to person. Whenever a person coughs, sneezes or even talks, tiny droplets are released into the air. These droplets can land in the mouths or noses of people close by. Additionally, these droplets may land on certain objects. People may become infected by touching objects with the virus on them and then touching their eyes, nose, or mouth. 

Is it contagious? 

Yes, the flu is contagious. An infected individual may pass the flu to someone else before they realize they are even sick. If possible, stay home when you are sick to prevent transmission of the illness. Most healthy adults may be able to infect others beginning one day before symptoms develop and up to five to seven days after becoming sick. Young children and those with a weakened immune system might be able to infect others for an even longer time. 

How severe is the flu? 

Severity of the flu is unpredictable and can vary from one season to the next, from person to person. The severity of a particular flu season will vary depending on a number of factors, including: the type of flu viruses spreading, how much and when the flu vaccine is available, how many people get vaccinated, and how well the flu vaccine is matched to flu viruses that are causing illness. 

Certain populations of people are at an increased risk for complications of the flu, such as dehydration, worsening of chronic medical conditions, pneumonia, ear infections, and sinus infections. These populations include: 

  • Adults 65 years of age or older 
  • Young children under the age of 5 years old (especially those under 2 years of age) 
  • Pregnant people 
  • People with certain health conditions (e.g., asthma, diabetes, or heart disease) 

When to seek medical attention 

While most people who get the flu can take care of themselves at home, others may be at risk for serious complications. Seeking emergency medical care immediately is advised for those experiencing: 

  • Trouble breathing/shortness of breath 
  • Cough or fever that begins to improve and then gets worse 
  • Chest pain 
  • Dizziness 
  • Worsening of existing medical conditions  
  • Severe weakness or muscle pain 
  • Seizures 

Additionally, children showing signs of dehydration or have bluish lips need medical attention immediately. 


Again, the best way to prevent the flu is by getting a flu vaccination. Each year, the flu vaccine provides individuals with protection from the three or four influenza viruses that are anticipated to be the most common flu viruses that year.  There are two different ways people can get the flu vaccine: through an injection and through a nasal spray. A health care provider can advise on which vaccine may be recommended.  

In addition to getting the flu vaccine, practicing healthy habits can also reduce the risk of getting sick. Frequent hand washing, avoiding close contact with people who are sick, avoiding touching your eyes, mouth, or nose, getting plenty of sleep, managing stress, and drinking plenty of fluids are all good strategies. 

Last reviewed/updated: March 11, 2021

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