The Flu (Influenza)

This information explains the flu (influenza), including how it’s spread and how you can lower your risk of getting it.

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What is the flu?

The flu is caused by a virus (germ) that affects your respiratory system (your nose, throat, and lungs) and can cause infection.

The flu can be a serious illness for people with cancer or other diseases, and for people with weakened immune systems. Your immune system is made up of cells, tissues, and organs that help your body fight off illness. Cancer and cancer treatments, such as chemotherapy, can weaken your immune system. This can make it hard for you to fight off the flu and may put you at a higher risk for other issues if you get sick with the flu.

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What should I know about the flu and COVID-19?

Because of the COVID-19 pandemic, it’s even more important to protect yourself from getting the flu. While we don’t know much about what happens if you get infected with both the flu and COVID-19, people who have cancer may be at higher risk for complications. This is why it’s important to get your flu shot.

If you have cancer or live with someone who does, you should protect yourself and your family by getting the flu shot. Remember to follow CDC guidelines, such as washing your hands for at least 20 seconds, keeping a safe distance of at least 6 feet from other people, and wearing a mask.

For more information about how to protect yourself against the flu, read the “What can I do to lower my risk of getting the flu or passing it on to others?” section of this resource.

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What are the signs of the flu?

If you have the flu, you may have 1 or more of the signs below:

  • Fever (a temperature above 100.4° F (38° C), or as directed by your healthcare provider)
  • Sore throat
  • Chills
  • Cough
  • Breathing problems (such as shortness of breath or chest tightness)
  • Headache
  • Runny nose
  • Body aches
  • Tiredness and general discomfort

Many symptoms of the flu are the same as COVID-19. If you think you have these symptoms, call your doctor right away.

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How does the flu spread?

The flu spreads through contact with droplets from the nose and throat of someone who is infected. The droplets carrying the virus are released into the air when the infected person coughs or sneezes. You can easily inhale (breathe in) these droplets and get an infection.

The flu can also spread when these droplets fall onto surfaces around an infected person. If you touch the surface and then touch your nose, mouth, or eyes, you could be infected.

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What can I do to lower my risk of getting the flu or passing it on to others?

  • Get the flu shot every year. Your healthcare provider will let you know if it’s safe for you to get a flu shot.
  • Ask family members and close friends to get the flu shot.
  • Always cough or sneeze into a tissue or your elbow, not your hand.
  • Wash your hands for at least 20 seconds or use an alcohol-based hand sanitizer often, especially after coughing or sneezing. Read our resource Hand Hygiene and Preventing Infection to learn how to clean your hands properly.
  • Don’t share items such as cups, drinking glasses, eating utensils, or toys.
  • Avoid close contact with anyone who has cold or flu symptoms.
  • If you have the flu, avoid close contact with others until your flu symptoms go away.

There are antiviral medications you can take that can help prevent or lessen your flu symptoms. Your doctor can prescribe these for you. These medicines shouldn’t replace a yearly flu shot.

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Where can I get the flu shot?

If you’re a patient at Memorial Sloan Kettering (MSK), you can get your flu shot at one of our MSK locations. Call your healthcare provider to schedule an appointment. If you can’t get to an MSK location or you aren’t an MSK patient, you can get the flu shot at your local pharmacy. Visit to find a location offering flu shots near you.

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When should I get my flu shot?

We recommend that you get your flu shot in September or October. It’s always a good time to get a flu shot but getting your shot in September or October can help protect you throughout the flu season.

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Will I get the flu from the flu shot?

No, flu shots don’t cause the flu. The most common side effects from the flu shot are soreness, redness, tenderness, and swelling in the area where you got your shot.

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What happens if I’m in the hospital and I have the flu?

If you have the flu while you’re in the hospital, we will need to follow special safety measures to stop the infection from spreading from person to person.

If you have the flu while you’re in the hospital:

  • You’ll be placed in a private room.
  • A sign will be posted on your door telling all staff  to clean their hands with soap and water or an alcohol-based hand sanitizer before going into and after leaving your room.
  • All staff  will need to wear a mask, yellow gown, and gloves while in your room. These are available outside of your room.
  • If you leave your room for tests, you must wear a mask, yellow gown, and gloves.
  • You won’t be able to walk around your unit, or go to the following areas of the hospital:
    • Pantry on your unit
    • Recreation center on M15
    • Pediatric recreation areas on M9 and the Pediatric Ambulatory Care Center (PACC)
    • Cafeteria
    • Main lobby
    • Any other public area of the hospital
    • You can have art or massage therapy in your room while following these safety measures.

You can stop following these safety measures when you can no longer pass the infection to others. Your healthcare team will let you know when it’s safe to do so.

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I have the flu. What should I do when I go to my outpatient appointments?

  • The day before your appointment, we will ask you to answer a short list of questions about your symptoms. You can answer these questions on your MyMSK patient portal account by going to or we will call you to ask these questions over the phone.
  • You’ll need to wear a mask over your mouth and nose during your entire appointment.
  • When you check in for your appointment, reception staff will ask you about your symptoms.
    • If you have any symptoms, a staff member will bring you to a private room where a healthcare provider will ask you more questions about your symptoms to help you get the care you need.
  • To keep patients and staff safe and healthy during the COVID-19 pandemic, we may change our visitor policy more often than usual. Visit for the most up-to-date information.
  • If you feel too sick to come in for your appointment, call your doctor right away to reschedule. You can also schedule a telemedicine visit instead. For more information about telemedicine visits, read our resource Telemedicine Visits at MSK.
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Where can I get more information about the flu?

If you have any questions, talk with your healthcare provider. You can also visit the following websites for more information:

Centers for Disease Control and Prevention

New York State Department of Health

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