Recombinant Influenza Vaccine (RIVs)

Flublok Quadrivalent (RIV4) [Protein Sciences] 0.5 mL prefilled syringe ≥18 yrs NR No IM
Flublok (RIV3) [Protein Sciences] 0.5 mL single-dose vial ≥18 yrs NR No IM

Abbreviations: IM = intramuscular; NR = not relevant (does not contain thimerosal); yrs = years.

RIV Hemagglutinin Content

  • RIVs contain 45µg of HA derived from each vaccine virus per 0.5mL dose (135µg total for RIV3 and 180 µg total for RIV4).

RIV Administration

  • RIV is administered intramuscularly.
    • Adults and older children: deltoid is the preferred site;
    • Infants and younger children: the anterolateral thigh is the preferred site.
  • Detailed guidance for administration sites and needle length is available in Best Practices Guidance of the Advisory Committee on Immunization Practices (ACIP) at General Best Practice Guidelines for Immunization.

RIV Contraindications and Precautions


  • History of severe allergic reaction to any component of the vaccine.
    • Information about vaccine components is located in package inserts from the manufacturer.


  • Moderate to severe acute illness with or without fever.
  • Guillain–Barré syndrome within 6 weeks following a previous dose of influenza
Vaccine Abbreviations
  • IIV = Inactivated Influenza Vaccine.
    • IIV3 = Trivalent Inactivated Influenza Vaccine;
    • IIV4 = Quadrivalent Inactivated Influenza Vaccine.
  • RIV = Recombinant Influenza Vaccine.
    • RIV3 = Trivalent Recombinant Influenza Vaccine;
    • RIV4 = Quadrivalent Recombinant Influenza Vaccine.
  • LAIV4 = Quadrivalent Live Attenuated Influenza Vaccine
  • IIV, RIV, and LAIV denote vaccine categories; numeric suffix denotes number of antigens in the vaccine,
  • When referring specifically to adjuvanted vaccine, the prefix “a” is used (e.g., aIIV3).
  • When referring specifically to cell culture-based vaccine, the prefix “cc” is used (e.g., ccIIV4).
  • When referring specifically to High-dose vs. Standard-dose vaccines, the prefixes “HD-” and “SD-” are used (e.g., HD-IIV3 vs. SD-IIV3 and SD-IIV4).