WHAT IS THE FLU?

WHAT IS THE FLU?

Influenza—the flu, for short—is a highly contagious respiratory infection caused by the influenza virus. The flu can cause mild illnesses, but for some it can also be serious—even deadly—especially for people over 65, young children, pregnant women, and people with certain chronic health conditions.

HOW IS FLU SPREAD?

The flu spreads easily from person to person, and you can catch it when someone who is infected coughs or sneezes—or even if you touch a recently contaminated surface or object that has the flu virus on it and then touch your nose, eyes, or mouth.

Icon of a person sneezing toward another person
Icon of a person sneezing toward another person
Young woman wearing a hooded parka, and knit scarf and gloves, holding a tissue to her nose.
Young woman wearing a hooded parka, and knit scarf and gloves, holding a tissue to her nose.
WHEN IS FLU SEASON?

In the U.S., flu season occurs in the fall and winter. Flu activity typically peaks between December and February, but it can last up until May.

The Centers for Disease Control and Prevention (CDC) monitors flu activity year-round in the U.S. and posts a weekly report that includes information on what viruses are circulating, and details on flu-related hospitalizations and deaths.

Click here for the most recent report.

TYPES OF INFLUENZA

There are 4 types of influenza viruses: A, B, C, and D. According to the CDC, types A and B are responsible for seasonal flu epidemics.

TYPE A

is the most common—and often the most harmful—form of influenza. Type A viruses can spread from animals to humans.

Subtypes of type A have caused some of the deadliest flu pandemics in history.

For example:
H1N1, which caused swine flu in 2009
H3N2, which caused Hong Kong flu in 1968

TYPE B

is also highly contagious but can only spread among humans.

Type B viruses can also cause outbreaks of seasonal flu.

3D illustration of a flu virus at a magnified view as if taken with an electron scanning microscope.
3D illustration of a flu virus at a magnified view as if taken with an electron scanning microscope.

DIFFERENT FLU SHOTS ARE APPROVED FOR DIFFERENT AGES

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FIND ONE NEAR YOU

What are Fluzone® Quadrivalent, Flublok® Quadrivalent, and Fluzone® High-Dose Quadrivalent?

Fluzone Quadrivalent, Flublok Quadrivalent, and Fluzone High-Dose Quadrivalent are vaccines indicated for immunization against disease caused by influenza A and B strains contained in the vaccine. Fluzone Quadrivalent is given to people 6 months of age and older. Flublok Quadrivalent is given to people 18 years of age and older. Fluzone High-Dose Quadrivalent is given to people 65 years of age and older.

IMPORTANT SAFETY INFORMATION

Fluzone Quadrivalent, Flublok Quadrivalent, and Fluzone High-Dose Quadrivalent should not be given to anyone who has had a severe allergic reaction to any component of the vaccine (including eggs or egg products for Fluzone Quadrivalent and Fluzone High-Dose Quadrivalent) or after previous dose of the vaccine. In addition, Fluzone Quadrivalent and Fluzone High-Dose Quadrivalent should not be given to anyone who has had a severe allergic reaction after previous dose of any influenza vaccine.

Tell your health care provider if you have ever had Guillain-Barré syndrome (severe muscle weakness) after a previous influenza vaccination.

If Fluzone Quadrivalent, Flublok Quadrivalent, and Fluzone High-Dose Quadrivalent are given to people with a compromised immune system, including those receiving therapies that suppress the immune system, the immune response may be lower than expected.

Vaccination with Fluzone Quadrivalent, Flublok Quadrivalent, and Fluzone High-Dose Quadrivalent may not protect all people who receive the vaccine.

For Fluzone Quadrivalent, in children 6 months through 35 months of age, the most common side effects were pain, tenderness, redness, and/or swelling where you got the shot; irritability, abnormal crying, general discomfort, drowsiness, loss of appetite, muscle aches, vomiting, and fever. In children 3 years through 8 years of age, the most common side effects were pain, redness, and/or swelling where you got the shot; muscle aches, general discomfort, and headache. In adults 18 years and older, the most common side effects were pain where you got the shot; muscle aches, headache, and general discomfort.

For Flublok Quadrivalent, in adults 18 through 49 years of age, the most common side effects were tenderness, and/or pain where you got the shot; headache, tiredness, muscle aches, and joint pain. In adults 50 years of age and older the most common side effects were tenderness, and/or pain where you got the shot; headache and tiredness.

For Fluzone High-Dose Quadrivalent, in adults 65 years of age and older, the most common side effects were pain, redness, and/or swelling where you got the shot; muscle aches, headache, and general discomfort.

For Fluzone Quadrivalent, Flublok Quadrivalent, and Fluzone High-Dose Quadrivalent, other side effects may occur.

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MAT-US-2007827 Last Updated: 09/2020