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Generic Name: influenza virus vaccine (injection) (in floo ENZ a VYE rus VAK seen)
Brand Names: Flublok, Flublok Quadrivalent

Medically reviewed by P. Thornton, DipPharm Last updated on Aug 2, 2019.

What is Flublok?

Flublok is used to prevent infection caused by influenza virus. Flublok is a new class of influenza virus vaccine made by modern DNA and cell culture technology to produce the right protective ingredients for vaccination. The vaccine is redeveloped each year to protect against specific strains of flu virus.

Influenza (commonly known as "the flu") is a serious disease caused by a virus. Influenza virus can spread from one person to another through small droplets of saliva that are expelled into the air when an infected person coughs or sneezes. The virus can also be passed through contact with objects the infected person has touched, such as a door handle or other surfaces.

Flublok contains recombinant proteins which work as antigens to help your body to develop immunity to the disease. It does not contain egg protein, thiomerosal (mercury derivative), latex, anitbiotics, formaldehyde, gelatin, or live influenza virus.

Flublok will not treat an active infection that has already developed in the body.

Flublok is for use in adults 18 years and older.

Becoming infected with influenza is much more dangerous to your health than receiving Flublok. Influenza causes thousands of deaths each year, and hundreds of thousands of hospitalizations. However, like any medicine, Flublok can cause side effects but the risk of serious side effects is extremely low.

Like any vaccine, Flublok may not provide protection from disease in every person. Flublok will not prevent illness caused by avian flu ("bird flu").

Important information

Becoming infected with influenza is much more dangerous to your health than receiving this vaccine. However, like any medicine, Flublok can cause side effects but the risk of serious side effects is extremely low.

Before receiving this vaccine

You may not be able to receive Flublok if you have:

  • a history of severe allergic reaction to a flu vaccine; or
  • a history of Guillain-Barre syndrome (within 6 weeks after receiving a flu vaccine).

To make sure influenza virus injectable vaccine is safe for you, tell your doctor if you have ever had:

  • bleeding problems;
  • a neurologic disorder or disease affecting the brain (or if this was a reaction to a previous vaccine);
  • a history of seizures;
  • a weak immune system caused by disease, bone marrow transplant, or by using certain medicines or receiving cancer treatments; or
  • an allergy to latex.

You can still receive a vaccine if you have a minor cold. In the case of a more severe illness with a fever or any type of infection, wait until you get better before receiving Flublok.

The Centers for Disease Control and Prevention recommends that pregnant women get a flu shot during any trimester of pregnancy to protect themselves and their newborn babies from flu. The nasal spray form of influenza vaccine is not recommended for use in pregnant women.

It is not known whether influenza virus vaccine passes into breast milk or if it could harm a nursing baby. Do not receive Flublok without telling your doctor if you are breast-feeding a baby.

How is Flublok given?

Flublok is not for use in children. Your child's doctor can recommend the best influenza virus vaccine for your child.

Flublok is given as an injection (shot) into a muscle. You will receive this injection in a doctor's office or other clinic setting.

You should receive a flu vaccine every year. Your immunity will gradually decrease over the 12 months after you receive the influenza virus vaccine.

Flublok vaccine is usually given in October or November. Some people may need to have their vaccines earlier or later. Follow your doctor's instructions.

What happens if I miss a dose?

Since flu shots are usually given only one time per year, you will most likely not be on a dosing schedule. Call your doctor if you forget to receive your yearly flu shot in October or November.

What happens if I overdose?

An overdose of Flublok is unlikely to occur.

What should I avoid before or after receiving Flublok?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Flublok side effects

Flublok will not cause you to become ill with the flu. However, you may have flu-like symptoms at any time during flu season that may be caused by other strains of influenza virus.

You should not receive a booster vaccine if you had a life-threatening allergic reaction after the first shot.

Keep track of any and all side effects you have after receiving Flublok. If you ever need to receive influenza virus vaccine in the future, you will need to tell your doctor if the previous shot caused any side effects.

Get emergency medical help if you have signs of an allergic reaction to Flublok: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • a light-headed feeling, like you might pass out;
  • severe weakness or unusual feeling in your arms and legs (may occur 2 to 4 weeks after you receive the vaccine);
  • high fever;
  • seizure (convulsions); or
  • unusual bleeding.

Common Flublok side effects may include:

  • low fever, chills;
  • redness, bruising, pain, swelling, or a lump where the vaccine was injected;
  • headache, tired feeling; or
  • joint or muscle pain.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report vaccine side effects to the US Department of Health and Human Services at 1-800-822-7967.

What other drugs will affect Flublok?

Before receiving Flublok, tell your doctor if you are using:

  • phenytoin;
  • theophylline; or
  • a blood thinner such as warfarin, Coumadin.

Also tell the doctor if you have recently received drugs or treatments that can weaken the immune system, including:

  • an oral, nasal, inhaled, or injectable steroid medicine;
  • medications to treat psoriasis, rheumatoid arthritis, or other autoimmune disorders--azathioprine, etanercept, leflunomide, and others; or
  • medicines to treat or prevent organ transplant rejection--basiliximab, cyclosporine, muromonab-CD3, mycophenolate mofetil, sirolimus, tacrolimus.

If you are using any of these medications, you may not be able to receive the vaccine, or may need to wait until the other treatments are finished.

This list is not complete. Other drugs may affect influenza virus injectable vaccine, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Flublok only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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