What is the Flu?

What is the Flu?

Influenza, also known as the flu, is a respiratory infection caused by a virus that affects the nose, throat, and sometimes the lungs. For some people, flu symptoms can be mild, but for others, the symptoms can be severe and possibly life-threatening.

There are two main types of flu viruses: A and B. These viruses spread easily and are responsible for seasonal epidemics each year. Research shows that the flu infects about 8% of Americans annually, but this number fluctuates depending on the season.

The best way to reduce the risk of flu and its potential complications is by getting vaccinated each year.

COVID-19 vs. flu vs. common cold

The flu, the common cold, and COVID-19 are all illnesses caused by viral infections. Though they are all infectious diseases caused by different viruses, symptoms of these three illnesses are similar and can include headache, sore throat, runny nose, congestion, and body aches.

The flu and the common cold are often confused, but flu symptoms often arise more quickly than those of the common cold. The flu also typically produces more severe symptoms than the common cold, including fever, vomiting, and diarrhea. Though a cold can cause a fever, it is uncommon.

A distinct symptom of COVID-19 is a loss of taste and or smell. Studies show that it can take longer for people infected with COVID-19 to show symptoms, and they can remain contagious for longer periods than those infected with the flu. Both COVID-19 and the flu can cause fever, body aches, and diarrhea, so testing is needed to confirm a diagnosis.

Signs & Symptoms of the Flu


Knowing the symptoms of the flu is important so you can receive treatment as early as possible. Signs and symptoms of the influenza virus may include:

  • Fever or feeling feverish/chills
  • Cough
  • Sore throat
  • Sneezing
  • Runny or stuffy nose
  • Muscle or body aches
  • Headache
  • Fatigue (tiredness) 
  • Shortness of breath
  • Some people may have vomiting and diarrhea (though this is more common in children than adults)

Not everyone experiences all of these symptoms when they are infected. Some people may not have a fever, while others, especially young children, may experience high fevers that can reach temperatures above 102oF.

Most flu symptoms will fade within four to seven days, though some fatigue and weakness may linger for longer. Contact your primary care physician immediately if your symptoms worsen, if you experience ongoing symptoms, or if you are at risk of developing complications due to the flu.

What Causes the Flu?


The flu is caused by a virus that can be spread through the air when an infected person coughs, sneezes, or talks. The flu can also be spread by touching the mouth, nose, or eyes after touching an object or surface that has been contaminated with the virus.

The flu can spread before a person begins experiencing symptoms and for five to seven days after infection. However, children and people with compromised or weakened immune systems can remain contagious for longer periods of time.

When a person gets the flu virus, their immune system creates antibodies to fight off the virus. However, the flu virus is constantly changing and creating new strains. While your antibodies may protect against a strain you already had, they may not protect against different strains. This also applies to the antibodies that result from the flu vaccination.

Risk Factors for Flu Complications

Risk Factors

Anyone can get the flu, and serious related problems can happen at any age, but some people are at higher risk of flu-related complications. Risk factors include:

  • Age - The flu is more common in children between the ages of six months and five years, as well as adults over 65
  • Having a compromised or weakened immune system - People who have had organ transplants, are undergoing cancer treatments, or who have HIV or AIDS
  • Having a chronic or severe illness - People with diabetes, asthma, COPD, heart conditions. Liver disease, kidney disease)
  • Pregnancy - The risk increases after the first trimester
  • Weight - Those who have a body mass index of 40 or higher are at increased risk for flu complications
  • Race - Black, Hispanic, American Indian and Alaska Native (AI/AN) people have had consistently higher rates of severe flu outcomes

Flu Complications


Most flu cases will resolve on their own within a few days, but some can take up to two weeks. Certain high-risk individuals may develop flu complications after being infected, and these severe complications can require a longer recovery time. Complications may include:

Flu Prevention


The main preventative measure you can take to lower your risk of flu is to get the annual flu vaccine. The vaccine is available as a flu shot or by nasal spray, and works by exposing you to an inactive or weakened form of the flu virus. Your immune system produces antibodies in response to the exposure, which will help protect you from the flu if exposed to an active form of the virus.

Influenza viruses are constantly changing, which creates new “strains.” Getting the influenza vaccine each year will help reduce your risk of being infected with the most common strains, and it can also help reduce the risk of flu complications.

You can take several actions to help reduce the spread of the flu virus, including:

  • Washing hands frequently
  • Covering your nose and mouth when sneezing
  • Cleaning and disinfecting frequently touched surfaces regularly, especially when someone is ill
  • Avoid touching your nose, mouth, or eyes
  • Eating healthy, drinking plenty of fluids, and getting enough rest, which can help boost your immune system
  • Avoid close contact with people who are sick
  • Staying home and avoiding close contact with others if you are experiencing flu symptoms to reduce the risk of infecting others
Get Care

Trust NewYork-Presbyterian for Flu Care

NewYork-Presbyterian offers medical care for your individual case by scheduling same-day appointments for critical needs, accepting a wide variety of insurances, and offering easy scheduling options, including early, late, and weekend hours. We refer our patients to our experienced medical specialists as needed, and we also utilize a patient portal, making it easy for you to connect with your team of medical professionals, view your medical records, and more.

Explore the treatment options that we offer and schedule an appointment or virtual urgent care visit with NewYork-Presbyterian or at one of our Medical Group locations today.