Influenza vaccine

Kathryn Dzintars, Pharm.D., BCPS
Pediatric Dosing Author: Taylor Imburgia, Pharm.D., BCPPS

VACCINE TYPE

Three major types are available in the U.S.:

  • Inactivated influenza vaccine, Trivalent (IIV3)
    • Available as a high-dose vaccination
  • Recombinant influenza vaccine, Trivalent (RIV3)
  • Live attenuated influenza vaccine, Trivalent (LAIV3)
  • >All 2025-26 Influenza season vaccines will be trivalent vaccines as the influenza B/Yamagata lineage is no longer circulating.

INDICATIONS

ACIP RECOMMENDATIONS

  • Universal vaccination is recommended for all individuals aged 6 months and older who are otherwise healthy and without contraindications to vaccination. No significant changes from earlier recommendations in the August 2025 ACIP recommendations.
    • Do not wait for a specific vaccine preparation if an appropriate vaccine is available.
    • Note: For the 2025-2026 season, the CDC recommends either the inactivated influenza vaccine (IIV), the recombinant influenza vaccine (RIV), or the LAIV (intranasal).
      • All vaccine formulations will be trivalent for the 2025-2026 influenza season. Quadrivalent vaccines are no longer produced as the influenza B/Yamagata lineage is no longer circulating.
        • Vaccine virus strains included in 2025–2026 U.S. formulations
          • U.S. egg-based influenza vaccines: A/Victoria/4897/2022(H1N1)pdm09-like virus, A/Croatia/10136RV/2023 (H3N2)-like a virus, B/Austria/1359417/2021-like (Victoria lineage) virus.
          • U.S. cell culture-based vaccine (ccIIV4) and recombinant (RIV4) influenza vaccines: A/Wisconsin/67/2022 (H1N1)pdm09-like virus, A/District of Columbia/27/2023 (H3N2)-like virus, B/Austria/1359417/2021 (Victoria lineage)-like virus.
  • For persons with a history of egg allergy:
    • All persons > 6 months of age with an egg allergy should receive an influenza vaccine with any otherwise appropriate vaccine for the recipient’s age and health status.
      • It is no longer recommended that individuals with an egg allergy, who experience symptoms other than urticaria (e.g., angioedema, anaphylaxis), be vaccinated in a monitored setting.
      • Egg allergy alone necessitates no additional safety measures for the influenza vaccine beyond those recommended for any vaccine recipient, regardless of the severity of the previous reaction to egg.
    • Refer to the Influenza Immunization and Chemoprophylaxis module for more information.
  • ACIP recommends that all adults over the age of 65 years receive any one of the HIGH-DOSE or adjuvanted influenza vaccines: HD-IIV3, RIV3 or aIIV3.
  • ACIP recommendations for solid organ transplant recipients have been updated to include HD-IIV3 and aIIV3 as acceptable options for influenza vaccination, in addition to the previously recommended, age-appropriate IIV3 vaccines.

OTHER INFORMATION

  • Inactivated influenza vaccine can be used for anyone 6 months and older.
  • For the 2024-2025 influenza season, vaccination providers may choose to administer LAIV4 as an option for eligible individuals. Although the recommendation for the 2025-2026 season has not been announced, it is likely to follow the same guidelines.
  • Flu vaccination in the era of COVID-19
    • Influenza vaccination for individuals over 6 months of age can reduce the prevalence of influenza, potentially decreasing symptoms that may be confused with COVID-19. Additionally, increasing influenza vaccination rates may mitigate the severity of influenza illness, reduce hospitalizations, and decrease intensive care unit admissions.
    • For individuals with an acute illness suspected or confirmed to have COVID-19, consider delaying influenza vaccination until the acute illness has resolved.
    • Guidance is available at https://www.cdc.gov/vaccines/pandemic-guidance/index.html

FORMS

brand name

preparation

manufacturer

route

form

dosage^

cost*

Afluria (6 months - 35 months)

Inactivated quadrivalent influenza vaccine Influenza

Seqiris

IM

Vial

(10 doses)

0.25 mL

$22.42

Afluria

( > 3 years)

Inactivated trivalent influenza vaccine Influenza

Seqirus

IM

Syringe

0.5 mL

$22.42

Fluarix Tririvalent (> 6 months)

Inactivated Trivalent influenza vaccine

GSK

IM

Syringe

0.5 mL

$20.49

FluBlok (> 9 years). Non-Egg Based.

Recombinant trivalent influenza vaccine, RIV4

Sanofi

IM

Syringe

0.5 mL

$68.09

Flucelvax (>2 years)

Inactivated trivalent influenza vaccine,

ccIIV3

(preservative-free, antibiotic-free)

Seqirus

IM

Syringe

Vial (10 doses)

0.5 mL

0.5 mL

$34.98

$34.98

Flulaval Trivalent (>6 months)

Inactivated Trivalent influenza vaccine

GlaxoSmithKline

IM

Syringe

0.5 mL

$20.49

FluMist† Trivalent (2-49 years)

Live attenuated influenza vaccine

Astra Zeneca

Intranasal

Intranasal sprayer

0.2 mL

$26.19

Fluzone

( >6 months)

Inactivated trivalent vaccine

Sanofi-Pasteur

IM

Syringe

Vial (10 doses)

0.5 mL

0.5 mL

$19.37

$18.24

Fluzone High Dose (for persons ≥ 65 years)

Inactivated

trivalent influenza vaccine

Sanofi-Pasteur

IM

Syringe

0.5 mL

$68.09

Fluad (> 65 years)

Adjuvanted inactivated trivalent influenza vaccine

Seqirus

IM

Syringe

0.5 mL

$79.17

†FluMist is now available for self-administration for recipients aged 18 - 49 years or administration by a caregiver ≥ 18 years of age for those aged 2 - 17 years.

*Prices represent the specified cost per unit and the "Average Wholesale Price" (AWP).
^Dosage is indicated in mg unless otherwise noted.

PATHOGEN DIRECTED PROTECTION

  • Influenza A and B
  • 2025 - 2026 season: removal of the influenza B/Yamagata lineage strain. All vaccines are trivalent formulations.
    • U.S. egg-based influenza vaccines: A/Victoria/4897/2022(H1N1)pdm09-like virus, A/Croatia/10136RV/2023 (H3N2)-like a virus, B/Austria/1359417/2021-like (Victoria lineage) virus
    • U.S. cell culture-based vaccine (ccIIV4) and recombinant (RIV4) influenza vaccines: A/Wisconsin/67/2022 (H1N1)pdm09-like virus, A/District of Columbia/27/2023 (H3N2)-like virus, B/Austria/1359417/2021 (Victoria lineage)-like virus.
  • No preferential recommendation is made for one influenza vaccine over another in prior recommendations, including those for children. However, people 65 years and older would prefer the high-dose or adjuvanted vaccine; the standard vaccine is acceptable if not available.
  • Approximately 10 - 14 days are required to acquire immunologic protection.
    • Seroconversion in 76% and 66% of adults ages 18-49 and 50-64, respectively.
    • Titers ≥ 1:40 were achieved in 100% and 94% of adults ages 18-49 and 50-64, respectively.

DOSE/ADMINISTRATION

Adult PRIMARY SERIES

  • It should be given before the onset of influenza in the community; vaccines are usually available by mid-to-late August. The preference is to vaccinate by the end of October.
  • For adults living with HIV
    • Annual seasonal influenza vaccination is recommended for all individuals with HIV, as per the general vaccination series. Do not use the live attenuated (Flumist) when the CD4 count is < 200 cells/mm3.

Pediatric and Adult Vaccines

Age Indication

Dosage

Afluria

Trivalent

6 - 35 months

> 36 months

0.25 mL IM

0.5 mL IM

Fluarix Trivalent

≥ 6 months

0.5 mL IM

Flucelvax Trivalent

≥ 6 months

0.5 mL IM

Flulaval Trivalent

≥ 6 months

0.5 mL IM

FluMist Trivalent

≥ 2 - 49 years

0.2 mL IN

(0.1 mL per nostril)

Fluzone Trivalent

> 6 months

0.5 mL IM

ADULT VACCINES ONLY

FluBlok Trivalent

> 18 years

0.5 mL IM

Fluzone HIGH DOSE Trivalent

> 65 years

0.5 mL IM

Fluad Adjuvant Trivalent

> 65 years

0.5 mL IM

Adult BOOSTER

  • Required each season due to reformulation based on recently circulating influenza strains.

Pediatric PRIMARY SERIES

It should be given before the onset of influenza in the community; vaccines are usually available by mid-to-late August. The preference is to vaccinate by the end of October.

Children: ages 6 months - 8 years, preferably before the start of the influenza season. See table.

  • Administer two doses ≥ 4 weeks apart if any of the following:
    • Patient’s first season of influenza immunization
    • The patient received ≤ 1 dose of the quadrivalent influenza vaccine before July 1, preceding the current influenza season.
    • If vaccination history is unknown
  • Ages 2-8 years: no preference for any vaccine for healthy children without contraindications
  • See table for age- and vaccine-specific dosing.

Pediatric BOOSTER

  • Required each season due to reformulation based on recently circulating influenza strains.

ADVERSE DRUG REACTIONS

GENERAL

  • Intranasal LAIV vaccine is not recommended in children < 24 months of age because of the increased risk of hospitalization and wheezing.

COMMON

  • IIV:
    • Soreness at the injection site, usually > 2 days in ~30%
    • Injection site reactions (mild, transient) were reported in 36% of patients receiving Fluzone High-Dose (compared to 24% with standard Fluzone).
  • LAIV: runny nose/nasal congestion; headache, cough, and sore throat incidence were comparable to placebo.

OCCASIONAL

  • IIV: fever and malaise: 1.1% reported moderate to severe fevers with Fluzone High-Dose (compared to 0.3% with standard Fluzone).
  • LAIV: wheezing (especially in children 6-11 months). Avoid Flumist in children aged < 5 years with asthma or wheezing episodes in the previous 12 months.

RARE

  • ALL:
    • Guillain-Barré syndrome: an estimated 8 excess cases of GBS per 1 million vaccinations. The rate of adverse events from the pandemic vaccine is similar to that found in seasonal influenza vaccines.
    • Allergy: hives, angioedema, asthma.
    • Ocular and respiratory symptoms: red eyes, cough, wheeze, chest tightness, difficulty breathing, facial swelling, and sore throat (associated with a formulation available in Canada during the 2000-2001 season).
  • IIV: febrile seizure reported in 5-9 cases/1000 vaccinated children < 5 yrs old, with most seizures occurring in children < 3 yrs old when they received IIV (CSL Biotherapies) in Australia.

VACCINE/DRUG INTERACTIONS

  • Immunosuppressive therapies (corticosteroids, alkylating drugs, antimetabolites, and radiation): Do not co-administer LAIV. This may theoretically increase the risk of disseminated infection.
  • It can be co-administered with the pneumococcal vaccine and the COVID vaccinations (Comirnaty, Spikevax, Novavax). In infants and children < 24 months, IIV can be co-administered with nirsevimab (Beyfortus) if indicated.
  • There have been reports of the influenza vaccine inhibiting the clearance of warfarin, theophylline, and phenytoin; however, controlled studies have yielded inconsistent results.
  • The attenuated intranasal influenza vaccine should not be administered until 48 hours after cessation of antiviral compounds. Antiviral drugs should not be administered for at least 2 weeks after receiving the live attenuated intranasal influenza vaccine.

CONTRAINDICATIONS

  • Egg allergy is no longer a contraindication to receipt of the influenza vaccine. It is no longer recommended that individuals with an egg allergy who experience symptoms other than urticaria (e.g., angioedema, anaphylaxis) be vaccinated in a monitored setting. Egg allergy alone necessitates no additional safety measures for the influenza vaccine beyond those recommended for any vaccine recipient, regardless of the severity of the previous reaction to egg.
  • LAIV: a history of hypersensitivity to vaccine components, children and adolescents (5-17 years of age) receiving aspirin, individuals with a history of Guillain-Barré syndrome, and individuals with immune deficiency diseases.
    • Children aged 6 to 12 months may have a higher rate of wheezing and hospitalization with LAIV.

IMMUNE RESPONSE

  • 6 months- 8 years: 86% had an antibody response with 2 doses, but only 27% with 1 dose.
    • The ACIP in 2024 emphasized the importance of administering two doses of vaccine to all children aged 6 months to 8 years who have not previously received either live or attenuated influenza vaccine.
      • Doses should be separated by at least 4 weeks. Second doses given up to 4 days early are considered acceptable.
      • According to the AAP, doses do not need to be from the same brand. If appropriate for the child’s age and health status, they may receive IIV and LAIV in the same season.
      • Children aged 8 years who require two doses of vaccine should receive both doses, even if the child turns 9 years old between the first and second doses.
  • Adults >65 years: Fluzone High-Dose elicited significantly higher hemagglutination inhibition (HI) titers against all three influenza virus strains. Compared to the standard Fluzone vaccine, the clinical effectiveness of the high-dose Fluzone vaccine appears more efficacious; however, no preferential recommendation (yet) has been made for high-dose Fluzone over standard-dose IIV.

CLINICAL EFFICACY

  • Vaccine efficacy depends on the match of epidemic and vaccine strains; it has been consistently well-matched over the last decade. Prevention efficacy:
    • Young adults or healthy elderly: ~70%.
    • Elderly in nursing homes: 30-40%, but reduces influenza mortality by 80%.
    • Vaccine efficacy may be decreased in the elderly and in immunosuppressed individuals.
    • High-dose vaccine (age > 65 yrs): relative efficacy, 24.2% compared to SIV, suggesting enhanced protection with HD vaccine.
  • In adults, intranasally administered live attenuated vaccine resulted in a 40.9% reduction in febrile upper respiratory tract illnesses during a season with a poor match of epidemic and vaccine influenza strains.

OTHER INFORMATION

  • Estimated vaccination coverage remains < 50% among all patients for whom routine annual vaccination is recommended, including young children and adults with risk factors for influenza complications, healthcare personnel (HCP), and pregnant women.
  • Influenza is a major infectious cause of death in the U.S. (3,000 to 80,000 annually); most are elderly, in nursing homes, or have chronic diseases.
  • Providing the vaccine to healthy adults generally reduces URIs and employee absenteeism, but conflicting data on cost-effectiveness.
  • Healthcare workers should be vaccinated to protect patients and other healthcare workers. If given FluMist within 7 days post-administration, they must avoid high-risk patient contact.
  • LAIV is shipped refrigerated and should be kept refrigerated (35-46°F).
  • Children with asthma or reactive airway disease, persons with underlying medical conditions with a higher risk for influenza complications, children aged 6-23 months, and persons aged >49 years should not receive LAIV.
  • Serious flu-related complications have been reported in obese patients and post-partum women.
  • Flu vaccination in the era of COVID-19
    • Influenza vaccination for individuals over 6 months of age can reduce the prevalence of influenza, potentially decreasing symptoms that may be confused with COVID-19. Additionally, increasing influenza vaccination rates may mitigate the severity of influenza illness, reduce hospitalizations, and decrease intensive care unit admissions.
    • For individuals with an acute illness suspected or confirmed to have COVID-19, consider delaying influenza vaccination until the acute illness has resolved.
    • Guidance is available at https://www.cdc.gov/vaccines/pandemic-guidance/index.html

Basis for recommendation

  1. Grohskopf LA, Blanton LH, Ferdinands JM, et al. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices - United States, 2025-26 Influenza Season. MMWR Morb Mortal Wkly Rep. 2025;74(32):500-507.  [PMID:40879559]

    Comment: Annual update from ACIP for recommendations for flu vaccination for the 2025-26 season. Notable updates include a substitution for the H3N2 component of the vaccine, expansion of approval for FluBlok to individuals 9 years of age and older (previously 18 years of age), and the recommendation for FluMist to be available for self-administration. Additionally, all adults should receive a vaccine that is free of thimerosal as a preservative.

  2. American Academy of Pediatrics, Recommendations for Prevention and Control of Influenza in Children, 2025–2026: Policy Statement. https://doi.org/10.1542/peds.2025-073620 accessed 9/5/2025; published as prepublication 7/28/2025

    Comment: Annual recommendations from the Committee on Infectious Diseases of the American Academy of Pediatrics for the 2025-2026 season. All children six months and older are still recommended.

Last updated: September 14, 2025