Recombinant Influenza (Flu) Vaccine

What is Recombinant Flu Vaccine?

Recombinant influenza (flu) vaccines are produced using recombinant technology. This method does not require an egg-grown vaccine virus and does not use chicken eggs in the production process.

Recombinant flu vaccine was first licensed by the FDA in the United States in 2013. Currently, the recombinant flu vaccine and the cell culture-based flu vaccine are the only egg-free flu vaccines licensed for use in the United States.

There is one quadrivalent recombinant flu shot (Flublok Quadrivalent) available for the 2021–2022 influenza season.

How does Recombinant flu vaccine differ from the other approved flu vaccines?

Recombinant flu vaccines do not use the flu virus or chicken eggs in the manufacturing process. See How Influenza (Flu) Vaccines Are Made for more information.

Who can get Flublok Quadrivalent?

Flublok Quadrivalent is licensed for use in people 18 years and older.

Who should not get Flublok Quadrivalent?

People who are not within the FDA-approved age range (those younger than 18 years) and who have had severe allergic reactions to any ingredient of the vaccine should not get Flublok Quadrivalent.

What are the possible benefits of recombinant flu vaccines?

Because recombinant flu vaccine is not dependent on an egg supply, the recombinant influenza vaccine manufacturing process might be faster than that of egg-based vaccines in the event of a pandemic or shortage of the eggs needed to grow influenza viruses. This process is not limited by the selection of vaccine viruses that are adapted for growth in eggs. It also avoids mutations that can occur when viruses are grown in eggs, which can sometimes affect how well the finished vaccine works. A 2019 study in Hong Kong showed that recombinant flu vaccination resulted in a greater antibody response in adults 65 and older compared to traditional flu vaccines. Although increased antibody response following flu vaccination does not guarantee better clinical protection, additional studies to determine the possible benefits of recombinant flu vaccines in this age group are warranted.

Learn more about the recombinant flu vaccine manufacturing process on CDC’s How Flu Vaccines are Made.

Is this vaccine safe? Are there any side effects that could occur?

In clinical studies, the safety of recombinant flu vaccines was comparable to that of other injectable flu vaccines.  The most common side effects reported after receipt of Flublok Quadrivalent were similar to those reported for other injectable vaccines and include pain and tenderness at the injection site, headache, fatigue, and muscle or joint aches.

For more information see the Flublok Quadrivalent package insertexternal icon.

Special Consideration Regarding Egg Allergy

People with egg allergies can receive any licensed, recommended age-appropriate influenza (flu) vaccine (IIV4, RIV4, or LAIV4) that is otherwise appropriate.  People who have a history of severe egg allergy (those who have had any symptom other than hives after exposure to egg) should be vaccinated in a medical setting, supervised by a health care provider who is able to recognize and manage severe allergic reactions.

Two completely egg-free (ovalbumin-free) flu vaccine options are available: quadrivalent recombinant vaccine and quadrivalent cell-based vaccine.