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Influenza Virus Vaccine (Recombinant)

Medically reviewed by Last updated on Feb 7, 2019.


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Index Terms

  • Flublok Quadrivalent
  • Influenza Vaccine
  • Quadrivalent Recombinant Hemagglutinin (rHA) Vaccine
  • Recombinant Influenza Vaccine, Quadrivalent
  • RIV
  • RIV4

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product

Solution, Intramuscular [preservative free]:

Flublok: (0.5 mL [DSC]) [no egg protein]

Flublok: (0.5 mL [DSC]) [thimerosal free]

Solution Prefilled Syringe, Intramuscular [preservative free]:

Flublok Quadrivalent: 0.5 mL (0.5 mL) [egg free]

Brand Names: U.S.

  • Flublok Quadrivalent
  • Flublok [DSC]

Pharmacologic Category

  • Vaccine
  • Vaccine, Recombinant


Promotes immunity to seasonal influenza virus by inducing specific antibody production. Preparations from previous seasons must not be used.

Onset of Action

Most adults have antibody protection within 2 weeks of vaccination (CDC/ACIP [Grohskopf 2018]).

Duration of Action

Vaccine effectiveness declines at a variable rate, depending on virus subtypes, patient age, and other confounding factors (CDC/ACIP [Grohskopf 2018]).

Use: Labeled Indications

Influenza disease prevention: Active immunization against influenza disease caused by influenza virus subtypes A and type B contained in the vaccine in persons 18 years of age and older

The Advisory Committee on Immunization Practices (ACIP) recommends routine annual vaccination with seasonal influenza vaccine for all persons ≥6 months who do not otherwise have contraindications to the vaccine. ACIP recommends use of any age and risk factor appropriate product and does not express any preference for an influenza vaccine product. Persons ≥18 years may receive vaccination with the recombinant influenza vaccine (RIV). In addition to RIV, other products are available for certain patient populations: Persons ≥6 months of age may receive the trivalent inactivated influenza vaccine (IIV3) or the quadrivalent inactivated influenza vaccine (IIV4). Live attenuated influenza vaccine (LAIV4) is also an option for the 2018-2019 influenza season (CDC/ACIP [Grohskopf 2018]). ACIP does not express any preference for an influenza vaccine product in appropriate patients (CDC/ACIP [Grohskopf 2018]).

When vaccine supply is limited, target groups for vaccination (those at higher risk of complications from influenza infection and their close contacts) include the following (CDC/ACIP [Grohskopf 2018]): Note: Only use RIV if appropriate.

• All infants and children 6 to 59 months of age

• Persons ≥50 years of age

• Infants, children, and adolescents (6 months to 18 years of age) who are receiving long-term aspirin or salicylate therapy, and therefore, may be at risk for developing Reye syndrome after influenza

• Residents of nursing homes and other long-term care facilities

• Patients with chronic pulmonary disorders (including asthma) or cardiovascular systems disorders (except isolated hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus)

• Persons who have immunosuppression due to any cause (including immunosuppression caused by medications or HIV)

• Infants, children, and adolescents (6 months to 18 years of age) who are receiving long-term aspirin or salicylate therapy, and therefore, may be at risk for developing Reye syndrome after influenza

• Women who are or will be pregnant during the influenza season

• Health care personnel including students in these professions who will have contact with patients

• Household contacts (including children) and caregivers of neonates, infants, and children <5 years (particularly neonates and infants <6 months) and adults ≥50 years

• Household contacts (including children) and caregivers of persons with medical conditions that put them at higher risk of severe complications from influenza infection

• American Indians/Alaska Natives

• Morbidly obese (BMI ≥40)


Severe allergic reaction (eg, anaphylaxis) to any component of the vaccine

Dosing: Adult

It is important to note that influenza seasons vary in their timing and duration from year to year. In general, vaccination should begin soon after the vaccine becomes available (and, if possible, by the end of October) and prior to onset of influenza activity in the community. However, vaccination should continue throughout the influenza season as long as vaccine is available. The CDC does not recommend revaccination later in the season for those persons who have already been fully vaccinated (CDC/ACIP [Grohskopf 2018]).

Immunization: IM: 0.5 mL/dose (1 per season)

Dosing: Geriatric

Refer to adult dosing.

Dosing: Pediatric

Influenza seasons vary in their timing and duration from year to year. In general, vaccination should begin soon after the vaccine becomes available (if possible, by the end of October) and prior to onset of influenza activity in the community; however, vaccination should continue throughout the influenza season as long as vaccine is available (CDC/ACIP [Grohskopf 2018]).

Immunization: Adolescents ≥18 years: IM: 0.5 mL per dose as a single dose per season.


IM: For IM administration only. Gently invert the syringe prior to affixing the needle. Inspect for particulate matter and discoloration prior to administration. Avoid use if visible particles or discoloration are present in the solution after shaking. Adults should be vaccinated in the deltoid muscle. Do not inject into the gluteal region or areas where there may be a major nerve trunk. Do not mix with other vaccines or injections; separate needles and syringes should be used for each injection. To prevent syncope related injuries, patients should be vaccinated while seated or lying down (ACIP [Kroger 2017]). US law requires that the date of administration, the vaccine manufacturer, lot number of vaccine, and the administering person's name, title, and address be entered into the patient's permanent medical record.

Unless otherwise indicated in product labeling, jet injectors should not be used to administer recombinant influenza vaccines. Currently, Afluria and Afluria Quadrivalent are the only influenza vaccines licensed in the US with data about use with a jet-injector device.

Note: For patients at risk of hemorrhage following intramuscular injection, the vaccine should be administered intramuscularly if, in the opinion of the physician familiar with the patient's bleeding risk, the vaccine can be administered by this route with reasonable safety. If the patient receives antihemophilia or other similar therapy, intramuscular vaccination can be scheduled shortly after such therapy is administered. A fine needle (23 gauge or smaller) can be used for the vaccination and firm pressure applied to the site (without rubbing) for at least 2 minutes. The patient should be instructed concerning the risk of hematoma from the injection. Patients on anticoagulant therapy should be considered to have the same bleeding risks and treated as those with clotting factor disorders (ACIP [Kroger 2017]).


Store between 2°C to 8°C (36°F to 46°F). Protect from light. Do not freeze. Discard if frozen.

Adverse Reactions

All serious adverse reactions must be reported to the US Department of Health and Human Services (DHHS) Vaccine Adverse Event Reporting System (VAERS) 1-800-822-7967 or online at In Canada, adverse reactions may be reported to local provincial/territorial health agencies or to the Vaccine Safety Section at Public Health Agency of Canada (1-866-844-0018).

Note: Older adults refers to adults ≥50 years of age


Central nervous system: Headache (older adults 10% to 17%), fatigue (13% to 15%)

Local: Pain at injection site (37%, older adults 19% to 32%)

Neuromuscular & skeletal: Myalgia (8% to 11%)

1% to 10%:

Central nervous system: Chills (older adults 5%)

Gastrointestinal: Nausea (4% to 6%)

Local: Injection site reactions (3% to 7%; includes redness, swelling and firmness)

Neuromuscular & skeletal: Arthralgia (older adults 6% to 8%)

Respiratory: Cough (1% to 2%), nasal congestion (1% to 2%), nasopharyngitis (1% to 2%), pharyngolaryngeal pain (1% to 2%), rhinorrhea (1% to 2%), upper respiratory tract infection (1% to 2%)

<1%, postmarketing and/or case reports: Anaphylactoid reaction, anaphylaxis, hypersensitivity, hypersensitivity reaction, pleuropericarditis


Concerns related to adverse effects:

• Anaphylactoid/hypersensitivity reactions: Immediate treatment (including epinephrine 1 mg/mL) for anaphylactoid and/or hypersensitivity reactions should be available during vaccine use (ACIP [Kroger 2017]).

• Syncope: Syncope has been reported with use of injectable vaccines and may result in serious secondary injury (eg, skull fracture, cerebral hemorrhage); typically reported in adolescents and young adults and within 15 minutes after vaccination. Procedures should be in place to avoid injuries from falling and to restore cerebral perfusion if syncope occurs (ACIP [Kroger 2017]).

Disease-related concerns:

• Acute illness: The decision to administer or delay vaccination because of current or recent febrile illness depends on the severity of symptoms and the etiology of the disease. Defer administration in patients with moderate or severe acute illness (with or without fever); vaccination should not be delayed for patients with mild acute illness (with or without fever) (ACIP [Kroger 2017]).

• Bleeding disorders: Use with caution in patients with a history of bleeding disorders (including thrombocytopenia); bleeding/hematoma may occur from IM administration; if the patient receives antihemophilia or other similar therapy, IM injection can be scheduled shortly after such therapy is administered (ACIP [Kroger 2017]).

• Guillain-Barré syndrome: Use with caution in patients with history of Guillain-Barré syndrome (GBS); patients with history of GBS have a greater likelihood of developing GBS than those without. As a precaution, the ACIP recommends that patients with a history of GBS and who are at low risk for severe influenza complications, and patients known to have experienced GBS within 6 weeks following previous vaccination should generally not be vaccinated (consider influenza antiviral chemoprophylaxis in these patients). The benefits of vaccination may outweigh the potential risks in persons with a history of GBS who are also at higher risk for severe complications of influenza. Influenza infection itself may cause Guillain-Barré syndrome (CDC/ACIP [Grohskopf 2018]). Recent studies of patients who received the trivalent inactivated influenza vaccine or the monovalent H1N1 influenza vaccine have shown the risk of GBS is lower with vaccination than with influenza infection (Baxter 2013; Greene 2013; Kwong 2013).

Concurrent drug therapy issues:

• Anticoagulant therapy: Use with caution in patients receiving anticoagulant therapy; bleeding/hematoma may occur from IM administration (ACIP [Kroger 2017]).

• Vaccines: In order to maximize vaccination rates, the ACIP recommends simultaneous administration (ie, >1 vaccine on the same day at different anatomic sites) of all age-appropriate vaccines (live or inactivated) for which a person is eligible at a single clinic visit, unless contraindications exist (ACIP [Kroger 2017]).

Special populations:

• Altered immunocompetence: Consider deferring immunization during periods of severe immunosuppression (eg, patients receiving chemo/radiation therapy or other immunosuppressive therapy [including high-dose corticosteroid]); may have a reduced response to vaccination. Inactivated vaccine (IIV or RIV) is preferred over live virus vaccine for household members, healthcare workers and others coming in close contact with severely-immunosuppressed persons requiring care in a protected environment (ACIP [Kroger 2017]; CDC/ACIP [Grohskopf 2018]). Inactivated vaccines should be administered ≥2 weeks prior to planned immunosuppression when feasible; inactivated vaccines administered during chemotherapy should be readministered after immune competence is regained (ACIP [Kroger 2017]; IDSA [Rubin 2014]).

• Pediatric: In a clinical trial of infants and children 6 months through 3 years of age, a decreased response to Flublok was reported compared to currently licensed US influenza vaccine for this population, suggesting that it would not be effective in children ≤3 years; safety and efficacy in older pediatric patients have not been established; use has not been studied.

Dosage form specific issues:

• Flublok Quadrivalent is an influenza vaccine produced using continuous insect cell lines. They are recombinant hemagglutinin (rHA) vaccines and do not use the influenza virus or eggs during the production process. ACIP states they may be used in persons with an egg allergy of any severity if otherwise appropriate (CDC/ACIP [Grohskopf 2018]).

Other warnings/precautions:

• Appropriate use: Use of this vaccine for specific medical and/or other indications (eg, immunocompromising conditions, hepatic or kidney disease, diabetes) is also addressed in the annual ACIP Recommended Immunization Schedules (refer to CDC schedule for detailed information). Specific recommendations for vaccination in immunocompromised patients with asplenia, cancer, HIV infection, cerebrospinal fluid leaks, cochlear implants, hematopoietic stem cell transplant (prior to or after), sickle cell disease, solid organ transplant (prior to or after), or those receiving immunosuppressive therapy for chronic conditions as well as contacts of immunocompromised patients are available from the IDSA (Rubin 2014).

• Effective immunity: Vaccination may not result in effective immunity in all patients. Response depends upon multiple factors (eg, type of vaccine, age of patient) and may be improved by administering the vaccine at the recommended dose, route, and interval. Vaccines may not be effective if administered during periods of altered immune competence (ACIP [Kroger 2017]).

• Previous season vaccines: Influenza vaccines from previous seasons must not be used (ACIP [Kroger 2017]; CDC/ACIP [Grohskopf 2018]).

Monitoring Parameters

Monitor for anaphylaxis and syncope for 15 minutes following administration (ACIP [Kroger 2017]). If seizure-like activity associated with syncope occurs, maintain patient in supine or Trendelenburg position to reestablish adequate cerebral perfusion.

Pregnancy Considerations

Information specific to the use of recombinant influenza vaccine (RIV) in pregnancy is limited (CDC/ACIP [Grohskopf 2018]).

Maternal influenza infection may be associated with adverse fetal events. Pregnant and postpartum women are also at an increased risk of complications from influenza infection.

Vaccination with an inactivated influenza vaccine is recommended for all females who are or will become pregnant during the influenza season; vaccination may be done during any trimester of pregnancy (ACOG 732 2018). Influenza vaccination with any licensed, recommended, age-appropriate, inactivated vaccine is recommended for all females who are or may become pregnant during the influenza season and who do not otherwise have contraindications to the vaccine (ACOG 2018; CDC/ACIP [Grohskopf 2018]).

Pregnant females should observe the same precautions as nonpregnant patients to reduce the risk of exposure to influenza and other respiratory infections (CDC/HHS 2017). When vaccine supply is limited, focus on delivering the vaccine should be given to females who are pregnant or will be pregnant during the flu season, as well as mothers of newborns and contacts or caregivers of children <5 years of age (CDC/ACIP [Grohskopf 2018]).

Women exposed to this vaccine during pregnancy may contact the Flublok pregnancy registry at 800-822-2463.

Patient Education

• Discuss specific use of vaccine and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience injection site pain or irritation, headache, muscle pain, joint pain, loss of strength and energy, chills, or nausea (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.

Further information

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