ACIP seasonal influenza vaccine recommendations | Image Credit: © Leigh Prather - © Leigh Prather - stock.adobe.com.

Background

Since 2010, routine, annual influenza vaccination for all people aged 6 months and older who do not have contraindications has been recommended by the Centers for Disease Control and Prevention (CDC) and the Advisory Committee on Immunization Practices (ACIP). In an Morbidity and Mortality Weekly Report (MMWR) from the CDC, the 2023-2024 recommendations have been updated for the 2024-2025 influenza season, which most commonly circulates from late fall through the early spring.

"During each of the [6] influenza seasons from 2010–11 through 2015–16, influenza vaccination prevented an estimated 1.6–6.7 million illnesses, 790,000–3.1 million outpatient medical visits, 39,000–87,000 hospitalizations, and 3,000–10,000 respiratory and circulatory deaths each season in the United States," authors of the MMWR wrote.

2024-2025 Updates

Composition of the 2024-2025 seasonal vaccines and updated recommendations for adult solid organ transplant recipients highlight the primary changes for the upcoming influenza season, according to MMWR.

The composition of this year's vaccines include an update to the influenza A(H3N2) component, as US-licensed vaccines will contain "hemagglutinin (HA) derived from 1) an influenza A/Victoria/4897/2022 (H1N1)pdm09-like virus (for egg-based vaccines) or an influenza A/Wisconsin/67/2022 (H1N1)pdm09-like virus (for cell culture-based and recombinant vaccines, 2) an influenza A/Thailand/8/2022 (H3N2)-like virus (for egg-based vaccines) or an influenza A/Massachusetts/18/2022 (H3N2)-like virus (for cell culture-based and recombinant vaccines), and 3) an influenza B/Austria/1359417/2021 (Victoria lineage)-like virus (for egg-based, cell culture-based, and recombinant vaccines)," stated the report.

The FDA has recommended that the seasonal influenza vaccine composition in the United States no longer include influenza B/Yamagata, as no confirmed detections in the global surveillance have been recorded since March 2020.

Persons at increased risk for severe illness

All children aged 6 months through 59 months of age are at increased risk of severe illness and complications from influenza according to the CDC, as are persons who are or will be pregnant during the influenza season.

Children and adolescents aged 6 months through 18 years of age who receive aspirin- or salicylate-containing medications and who might be at risk for experiencing Reye syndrome after influenza virus infection are also at increased risk.

Dose volume: Children aged 6 through 35 months

For children aged 6 months through 35 months of age, the CDC noted the following approved dose volumes for specific vaccines. Five trivalent inactivated influenza vaccines (IIV3s) are approved for children aged 6 months and older. These vaccines and approved doses are listed below:

• Afluria: 0.25 mL per dose. However, 0.25-mL prefilled syringes are no longer available. For children aged 6 through 35 months, a 0.25-mL dose must be obtained from a multidose vial.
• Fluarix: 0.5 mL per dose.
• Flucelvax: 0.5 mL per dose.
• FluLaval: 0.5 mL per dose.
• Fluzone: Either 0.25 mL or 0.5 mL per dose. Per the package insert, each dose can be given at either volume (55); however, 0.25-mL prefilled syringes are no longer available.

Those aged 3 years and older should receive 0.5 mL per dose. "Alternatively, healthy children aged ≥24 months (≥2 years) can receive LAIV3, 0.2 mL intranasally (0.1 mL in each nostril)," stated the CDC, who noted that trivalent live attenuated influenza vaccine (LAIV3) is not recommended for specific populations and is not approved for children aged younger than 2 years or adults older than 49 years.

Number of influenza doses: Children aged 6 months through 8 years

For this patient population, 2 doses of influenza vaccine with a minimum of 4 weeks apart during their first season of vaccination is required for optimal protection. The number of influenza doses needed for the upcoming season is determined by the following, according to the MMWR:

• "Those who have previously received ≥2 total doses of trivalent or quadrivalent influenza vaccine ≥4 weeks apart before July 1, 2024, require only 1 dose for the 2024–25 season. The previous 2 doses of influenza vaccine do not need to have been received in the same season or consecutive seasons."
• "Those who have not previously received ≥2 doses of trivalent or quadrivalent influenza vaccine ≥4 weeks apart before July 1, 2024, or whose previous influenza vaccination history is unknown, require 2 doses for the 2024–25 season." Those aged 6 months through 8 years who require 2 doses should receive their first dose as soon as possible, including during August if vaccines are available. This will allow the second dose, which must be administered 4 or more weeks after the first, to be administered by the end of October, ideally.
• For children aged 8 years who require 2 doses of vaccine, both doses should be administered even if the child turns 9 years of age between receipt of dose 1 and dose 2.

Influenza vaccination among pregnant persons

Reduced risk for respiratory illness and influenza among pregnant and postpartum persons as well as infants during the first months of life is associated with influenza vaccination during pregnancy, according to the CDC. Pregnant and postpartum persons are at higher risk for severe illness and complications from influenza, especially during the second and third trimesters.

IIV3 or trivalent recombinant influenza vaccine (RIV3) can be used among pregnant or postpartum persons during the influenza season. LAIV3 can be used postpartum but should not be used during pregnancy. Early vaccination in August can be considered for those who are in the third trimester during this month if the vaccine is available, as this can provide protection for the infant during the first months of life when they are too young to be vaccinated themselves.

"Although experience with the use of IIVs during pregnancy is substantial, data specifically reflecting administration of influenza vaccines during the first trimester are limited. Most studies have not noted an association between influenza vaccination and adverse pregnancy outcomes, including spontaneous abortion (miscarriage)," wrote the study authors of the MMWR.

Reference:

Grohskopf LA, Ferdinands JM, Blanton LH, Broder KR, Loehr J. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2024–25 Influenza Season. MMWR Recomm Rep 2024;73(No. RR-5):1–25. DOI: http://dx.doi.org/10.15585/mmwr.rr7305a1