Which flu vaccine to administer and when?

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Last updated: October 22, 2025View editorial policy

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Influenza Vaccine Recommendations: Type and Timing

For adults aged ≥65 years, preferentially administer any one of the following higher dose or adjuvanted influenza vaccines: quadrivalent high-dose inactivated influenza vaccine (HD-IIV4), quadrivalent recombinant influenza vaccine (RIV4), or quadrivalent adjuvanted inactivated influenza vaccine (aIIV4). 1

General Recommendations

  • All persons aged ≥6 months who do not have contraindications should receive routine annual influenza vaccination 1
  • For each recipient, a licensed and age-appropriate vaccine should be used 1
  • All seasonal influenza vaccines expected to be available in the United States are quadrivalent, containing hemagglutinin (HA) derived from one influenza A(H1N1)pdm09 virus, one influenza A(H3N2) virus, one influenza B/Victoria lineage virus, and one influenza B/Yamagata lineage virus 1

Timing of Vaccination

  • For most persons who need only 1 dose of influenza vaccine for the season, vaccination should ideally be offered during September or October 1
  • Vaccination should continue after October and throughout the season as long as influenza viruses are circulating and unexpired vaccine is available 1
  • For adults aged ≥65 years and pregnant persons in the first or second trimester: Avoid vaccination during July and August unless there is concern that vaccination later in the season might not be possible 1
  • Children aged 6 months through 8 years who require 2 doses should receive the first dose as soon as possible after vaccine is available, including during July and August 1

Vaccine Selection by Age Group

Children aged 6 months through 35 months

  • Appropriate dose volumes differ by product 1:
    • Afluria Quadrivalent: 0.25 mL per dose 1
    • Fluarix Quadrivalent: 0.5 mL per dose 1
    • Flucelvax Quadrivalent: 0.5 mL per dose 1
    • FluLaval Quadrivalent: 0.5 mL per dose 1
    • Fluzone Quadrivalent: Either 0.25 mL or 0.5 mL per dose 1

Children aged 36 months through 17 years

  • All IIV4s are administered at 0.5 mL per dose 1
  • Children aged 6 months through 8 years receiving influenza vaccine for the first time or who have not received a total of ≥2 doses before July 1,2022, require 2 doses separated by at least 4 weeks 1, 2

Adults aged 18 through 64 years

  • Standard-dose IIV4s, RIV4, or LAIV4 (if no contraindications) at 0.5 mL per dose 1

Adults aged ≥65 years

  • Preferentially receive any one of the following 1:
    • Quadrivalent high-dose inactivated influenza vaccine (HD-IIV4) - 0.7 mL per dose 1
    • Quadrivalent recombinant influenza vaccine (RIV4) - 0.5 mL per dose 1
    • Quadrivalent adjuvanted inactivated influenza vaccine (aIIV4) - 0.5 mL per dose 1
  • If none of these three vaccines is available, any other age-appropriate influenza vaccine should be used 1

Special Considerations

Children requiring 2 doses

  • Children aged 6 months through 8 years require 2 doses of influenza vaccine (separated by at least 4 weeks) if they 1, 2:
    • Have never received influenza vaccine before
    • Have not received a total of ≥2 doses of influenza vaccine before July 1,2022

Post-influenza infection vaccination

  • There is no required waiting period after influenza infection before administering the vaccine, only that the child has clinically recovered from the acute illness 2
  • Any age-appropriate influenza vaccine formulation can be used after recent infection 2

Co-administration with other vaccines

  • Co-administration of influenza vaccines with pneumococcal and/or COVID-19 vaccines is associated with lower risk of hospitalization and mortality 3

Route of Administration

  • IIV4s are administered intramuscularly (IM) 1
  • For adults and older children, the deltoid muscle is the preferred site 1
  • Infants and younger children should be vaccinated in the anterolateral thigh 1
  • LAIV4 is administered intranasally 1

Common Pitfalls to Avoid

  • Delaying vaccination unnecessarily after recovery from influenza may leave individuals vulnerable during peak influenza season 2
  • Using the wrong dose volume for children aged 6 through 35 months - check the specific product information 1
  • Administering LAIV within 48 hours of antiviral medication use (contraindicated) 4
  • Failing to recognize that children aged 6 months through 8 years may need two doses in their first vaccination season 1, 2
  • Delaying the second dose of influenza vaccine beyond the recommended interval for children who require two doses 2

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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