Should an adult aged 65 years or older, or a younger adult with immunocompromising conditions, receive the high‑dose inactivated influenza vaccine rather than the standard‑dose vaccine?

High-Dose or Adjuvanted Influenza Vaccines Are Preferentially Recommended for Adults ≥65 Years

Adults aged 65 years or older should preferentially receive high-dose inactivated influenza vaccine (HD-IIV), adjuvanted inactivated influenza vaccine (aIIV), or recombinant influenza vaccine (RIV) over standard-dose vaccines. 1, 2, 1

For Adults ≥65 Years: Clear Preferential Recommendation

The Advisory Committee on Immunization Practices (ACIP) explicitly recommends that adults ≥65 years preferentially receive one of three enhanced vaccines 1:

• High-dose IIV (HD-IIV3): Contains 60 μg hemagglutinin per strain (4× standard dose)
• Adjuvanted IIV (aIIV3): Contains MF59 adjuvant with standard antigen dose
• Recombinant IIV (RIV3): Contains 45 μg hemagglutinin per strain (3× standard dose)

Critical caveat: If none of these three enhanced vaccines is available at the time of the patient visit, administer any other age-appropriate influenza vaccine rather than delaying vaccination. 1

Evidence Supporting Enhanced Vaccines

The most robust evidence comes from large randomized trials demonstrating superior protection with enhanced vaccines 3, 4, 5:

• HD-IIV reduces influenza hospitalizations by 38-39% compared to standard-dose vaccine 3, 5
• Laboratory-confirmed influenza hospitalizations reduced by 31-32% 3, 5
• Cardiorespiratory hospitalizations reduced by 7.5-8% 3, 5
• All-cause hospitalizations reduced by 3-4% 3, 4, 5
• Pneumonia/influenza hospitalizations reduced by 11-22% 3, 4

Importantly, no significant difference in all-cause mortality was demonstrated, though hospitalization benefits are clinically meaningful 3, 4, 5.

Comparing Enhanced Vaccines to Each Other

Recent head-to-head evidence shows adjuvanted and high-dose vaccines perform equivalently 6. In a large cluster-randomized crossover trial of 429,595 adults ≥65 years, the relative vaccine effectiveness between adjuvanted and high-dose vaccines was only 1.5% (95% CI: -8.4% to 10.5%), indicating no meaningful difference 6.

Practical implication: Choose whichever enhanced vaccine is available—don't delay vaccination waiting for a specific formulation.

For Younger Adults with Immunocompromising Conditions

Solid Organ Transplant Recipients (Ages 18-64 on Immunosuppression)

HD-IIV3 or aIIV3 are acceptable options for solid organ transplant recipients aged 18-64 years receiving immunosuppressive medications, though there is no preference over other age-appropriate vaccines 1. This represents an unlabeled use, as these vaccines are FDA-approved only for adults ≥65 years.

Rheumatic Disease Patients on Immunosuppression

The American College of Rheumatology conditionally recommends high-dose or adjuvanted influenza vaccination over standard-dose for patients with rheumatic diseases who are:

• Age ≥65 years, OR
• Age >18 and <65 years taking immunosuppressive medications 7, 8

Important practical note: If high-dose or adjuvanted vaccine is unavailable during the clinic visit, or if insurance restrictions prevent coverage for patients <65 years, administer standard-dose vaccine immediately rather than delaying 7, 8. Two randomized trials in rheumatoid arthritis patients showed higher seroconversion rates with high-dose vaccination and no safety concerns 7, 8.

Diabetes Patients ≥65 Years

Recent evidence from the DANFLU-2 trial demonstrates that HD-IIV provides consistent benefit regardless of diabetes status 9. Among 332,438 participants, HD-IIV reduced cardiorespiratory, cardiovascular, and influenza hospitalizations similarly in those with and without diabetes. Interestingly, the benefit appeared greater in those with diabetes duration >5 years 9.

Algorithm for Vaccine Selection

For adults ≥65 years:

1. Offer HD-IIV, aIIV, or RIV (whichever is available)
2. If none available → give standard-dose vaccine immediately
3. Do not delay vaccination waiting for enhanced formulations

For adults 18-64 years with immunocompromising conditions:

1. Solid organ transplant on immunosuppression: HD-IIV or aIIV acceptable (no preference over standard-dose)
2. Rheumatic disease on immunosuppression: Preferentially offer HD-IIV or aIIV
3. If enhanced vaccines unavailable or insurance denies: Give standard-dose immediately

For all other adults 18-64 years:

• Standard-dose vaccine is appropriate

Common Pitfalls to Avoid

• Don't delay vaccination in July-August for most adults ≥65 years due to potential waning immunity, unless there's concern vaccination won't be possible later 2
• Don't withhold standard-dose vaccine if enhanced vaccines are unavailable—any vaccine is better than no vaccine 1, 7, 8
• Don't assume all enhanced vaccines are identical—they use different mechanisms (higher antigen dose vs. adjuvant vs. recombinant technology), but clinical outcomes are similar 6
• Insurance barriers for <65 years: Document medical necessity for immunocompromised patients when requesting enhanced vaccines 7, 8

Safety Profile

Enhanced vaccines show no significant difference in serious adverse events compared to standard-dose vaccines 3, 4. However, adjuvanted vaccines have greater reactogenicity (local injection site reactions, myalgia) 7, 8, which should be discussed with patients but does not contraindicate use.