Flublok Quadrivalent

  • Vaccines

Flublok Quadrivalent Generic Name & Formulations

General Description

Quadrivalent, recombinant hemagglutinin (virus types A and B); contains a total of 180mcg recombinant hemagglutinin per 0.5mL dose; formulation changes annually; soln for IM inj; egg-, antibiotic-, preservative-free.

Pharmacological Class

Influenza vaccine.

How Supplied

Single-dose prefilled syringes (0.5mL)—10


  • Store refrigerated between 2°C and 8°C (36°F and 46°F). Do not freeze. Discard if product has been frozen. Protect syringes from light. Do not use after expiration date shown on the label. 


Generic Availability


Mechanism of Action

Flublok Quadrivalent contains recombinant hemagglutinin (HA) proteins of the four strains of influenza virus specified by health authorities for inclusion in the annual seasonal vaccine. These proteins function as antigens which induce a humoral immune response, measured by hemagglutination inhibition (HI) antibody.

Flublok Quadrivalent Indications


Influenza immunization.

Flublok Quadrivalent Dosage and Administration


≥18yrs: 0.5mL by IM inj once in the deltoid.


3–<18yrs: not established.

Flublok Quadrivalent Contraindications

Not Applicable

Flublok Quadrivalent Boxed Warnings

Not Applicable

Flublok Quadrivalent Warnings/Precautions


Guillain-Barre syndrome within 6 weeks of previous flu vaccine. Immunosuppressed. Have appropriate treatment available to manage anaphylaxis. Pregnancy. Nursing mothers.


Managing Allergic Reactions

  • Appropriate medical treatment and supervision must be available to manage possible anaphylactic reactions following administration of the vaccine.

Guillain-Barré Syndrome

  • Carefully consider the potential benefits and risks to give Flublok Quadrivalent if Guillain-Barré Syndrome (GBS) has occurred within 6 weeks of previous influenza vaccination.

  • Evidence for a causal relation of GBS with subsequent vaccines prepared from other influenza viruses is unclear. If influenza vaccine does pose a risk, it is probably slightly more than one additional case per 1 million persons vaccinated.

Altered Immunocompetence

  • Immune response may be diminished if Flublok Quadrivalent is given to immunocompromised individuals, including those receiving immunosuppressive therapy.

Limitations of Vaccine Effectiveness

  • Afluria Quadrivalent may not protect all individuals.

Pregnancy Considerations

Pregnancy Exposure 

  • Pregnancy outcomes in women who have been exposed to Flublok Quadrivalent during pregnancy are being monitored. Sanofi Pasteur Inc. is maintaining a prospective pregnancy exposure registry to collect data on pregnancy outcomes and newborn health status following vaccination with Flublok Quadrivalent during pregnancy. Healthcare providers are encouraged to enroll women who receive Flublok Quadrivalent during pregnancy in Sanofi Pasteur Inc.'s vaccination pregnancy registry by calling 1-800-822-2463.

Risk summary

  • Data for Flublok (trivalent formulation) administered to pregnant women are relevant to Flublok Quadrivalent. 

  • There is insufficient data for Flublok Quadrivalent and Flublok (trivalent formulation) administered to pregnant women to inform of vaccine-associated risks in pregnancy.

Clinical Considerations

  • Disease-associated Maternal and/or Embryo-Fetal Risk: Pregnant women are at increased risk for complications due to influenza compared to nonpregnant women. Pregnant women with influenza may be at increased risk for adverse pregnancy outcomes, including preterm labor and delivery.

Nursing Mother Considerations

Risk Summary

  • It is not known whether Flublok Quadrivalent is excreted in human milk.

  • Consider the developmental and health benefits of breastfeeding with the mother’s clinical need for Flublok Quadrivalent and any potential adverse effects on the breastfed child from Flublok Quadrivalent or from the underlying maternal condition.

Pediatric Considerations

  • Safety and effectiveness of Flublok Quadrivalent have not been established in children 3 years to less than 18 years of age.

Flublok Quadrivalent Pharmacokinetics

See Literature

Flublok Quadrivalent Interactions


Concomitant vaccines: insufficient data (see full labeling). Immunosuppressants: may get suboptimal response.

Flublok Quadrivalent Adverse Reactions

Adverse Reactions

Inj site tenderness and pain, headache, fatigue, myalgia, arthralgia.

Flublok Quadrivalent Clinical Trials

Clinical Trials

Efficacy against Laboratory-Confirmed Influenza

Study 3

  • The efficacy of Flublok (trivalent formulation) is relevant to Flublok Quadrivalent.

  • The efficacy of Flublok (trivalent formulation) was based on a randomized, observer-blind, placebo-controlled trial which included 4648 participants 18 to 49 years of age. Participants were randomly assigned 1:1 to receive a single dose of Flublok (trivalent formulation) or placebo.

  • The primary efficacy endpoint of Study 3 was Centers for Disease Control-defined influenza-like illness (CDC-ILI) with a positive culture for an influenza virus strain antigenically resembling a strain represented in Flublok. CDC-ILI is defined as fever of ≥100°F oral accompanied by cough, sore throat, or both on the same day or on consecutive days. Attack rates and vaccine efficacy (VE), defined as the reduction in the influenza rate for Flublok relative to placebo, were calculated for the total vaccinated cohort (n=4648).  

  • The vaccine efficacy for Flublok (trivalent formulation) was 44.8% against all strains, regardless of antigenic match, isolated from any subject with an ILI, not necessarily meeting the CDC-ILI criteria.

Study 2

  • The efficacy of Flublok Quadrivalent was based on a randomized, observer-blind, active-controlled trial which included 8963 participants 50 years of age and older. Participants were randomly assigned 1:1 to receive a single dose of Flublok Quadrivalent or a US-licensed quadrivalent inactivated influenza vaccine (Comparator, Fluarix Quadrivalent).

  • Real-time polymerase chain reaction (rtPCR)–confirmed influenza was assessed by active and passive surveillance for influenza-like illness (ILI) beginning 2 weeks post-vaccination until the end of the influenza season, approximately 6 months post- vaccination. The primary efficacy endpoint of Study 2 was rtPCR-positive, protocol-defined ILI due to any strain of influenza.

  • The relative vaccine efficacy of Flublok Quadrivalent vs comparator against laboratory-confirmed influenza, regardless of antigenic similarity to vaccine antigens were as followed:

    • All rtPCR-positive influenza: 30% (95% CI, 10-47)

    • All rtPCR-positive influenza A: 36% (95% CI, 14-53)

    • All rtPCR-positive influenza B: 4% (95% CI, -72, 46)

    • All culture-confirmed protocol-defined ILI: 43% (95% CI, 21-59)


Immunogenicity of Flublok Quadrivalent

Study 1

  • The randomized, observer-blind, active-controlled, multicenter trial evaluated the immunogenicity of Flublok Quadrivalent compared with a US-licensed quadrivalent inactivated influenza vaccine (Fluarix Quadrivalent) in 1350 patients 18 to 49 years of age. Patients were randomly assigned 3:1 to receive Flublok Quadrivalent or comparator.

  • Post-vaccination immunogenicity was evaluated on sera obtained 28 days after administration of a single dose of study vaccine. Hemagglutination inhibition (HI) geometric mean titers (GMTs) were determined for the two vaccine groups for each vaccine antigen. Immunogenicity was compared by calculating the difference in seroconversion rates (SCR) and the ratios of GMTs of Comparator to Flublok Quadrivalent.

  • Flublok Quadrivalent met the success criterion for GMTs for 3 of the 4 antigens but not for the B/Victoria lineage antigen. Flublok Quadrivalent met the success criterion for SCRs for 3 of the 4 antigens but not for the B/Victoria lineage antigen

Flublok Quadrivalent Note

Not Applicable

Flublok Quadrivalent Patient Counseling

Patient Counseling

Inform the vaccine recipient of the potential benefits and risks of vaccination with Flublok Quadrivalent. Inform the vaccine recipient that: 

  • Flublok Quadrivalent contains non-infectious proteins that cannot cause influenza.

  • Flublok Quadrivalent stimulates the immune system to produce antibodies that help protect against the influenza viruses carrying the proteins contained in the vaccine, but does not prevent other respiratory infections. 

Instruct the vaccine recipient to report any adverse events to their healthcare provider and/or to the Vaccine Adverse Event Reporting System (VAERS). 

Provide the vaccine recipient with the Vaccine Information Statements which are required by the National Childhood Vaccine Injury Act of 1986 to be given prior to vaccination. These materials are available free of charge at the Centers for Disease Control (CDC) website (www.cdc.gov/vaccines). 

Encourage women who receive Flublok or Flublok Quadrivalent while pregnant to notify Sanofi Pasteur Inc. by calling 1-800-822-2463. 

Instruct the vaccine recipient that annual vaccination to prevent influenza is recommended.