INFLUENZA (FLU)

There are few changes to the influenza (flu) vaccination recommendations adopted by the Centers for Disease Control and Prevention (CDC) for the 2023–2024 season. The CDC recommends annual vaccination for everyone 6 months of age and older who does not have contraindications. For most persons who need only one dose of influenza vaccine for the season, vaccination should ideally be offered during September or October. However, vaccination should continue throughout the season as long as influenza viruses are circulating.

2023–24 Seasonal Flu Vaccine Recommendations

Flu viruses are continually changing. The composition of U.S. flu vaccines is reviewed annually by the U.S. Food and Drug Administration (FDA) Vaccines and Related Biological Products Advisory Committee and updated as needed to best match the flu viruses that research indicates will be most common during the upcoming season (CDC, 2023a). The composition of flu vaccines for the U.S. 2023–2024 season will contain the following:

Egg-based vaccines:

• An A/Victoria/4897/2022 (H1N1)pdm09-like virus (updated)
• An A/Darwin/9/2021 (H3N2)-like virus
• A B/Austria/1359417/2021 (B/Victoria lineage)-like virus
• A B/Phuket/3073/2013 (B/Yamagata lineage)-like virus

Cell- or recombinant-based vaccines:

• An A/Wisconsin/67/2022 (H1N1)pdm09-like virus (updated)
• An A/Darwin/6/2021 (H3N2)-like virus
• A B/Austria/1359417/2021 (B/Victoria lineage)-like virus
• A B/Phuket/3073/2013 (B/Yamagata lineage)-like virus

The main change in this season’s flu vaccine recommendations is related to administering flu vaccine to people with egg allergies. Most flu vaccines today continue to be produced using an egg-based manufacturing process and therefore contain a small amount of egg proteins, such as ovalbumin. The Advisory Committee on Immunization Practices (ACIP) recommends that persons ages ≥6 months with egg allergy receive the influenza vaccine. Any influenza vaccine (egg-based or non-egg-based) that is otherwise appropriate for the recipient’s age and health status can be used.

All vaccines should be administered in settings in which personnel and equipment needed for rapid recognition and treatment of acute hypersensitivity reactions are available. Egg allergy necessitates no additional safety measures for influenza vaccination beyond those recommended for any recipient of any vaccine, regardless of severity of previous reaction to egg (CDC, 2023a).

Persons who are pregnant or who might be pregnant during the influenza season should receive influenza vaccine. Any age-appropriate IIV4 or RIV4 may be given in any trimester. LAIV4 should not be used during pregnancy but can be used postpartum.

Approved ages and dose volumes for intramuscular influenza vaccines (IIV4s and RIV4) are listed in the table below.

INTRAMUSCULAR FLU VACCINE APPROVED AGES AND DOSAGES

Vaccine	Approved Ages	Dose Volume
* The approved dose volume per the package insert for Fluzone Quadrivalent is either 0.25 mL or 0.5 mL for ages 6–35 months, but 0.25mL prefilled syringes are not available. (ACIP, 2023)
Afluria quadrivalent	6–35 months ≥3 years	0.25 mL 0.5 mL
Fluarix quadrivalent	≥6 months	0.5 mL
Flulaval quadrivalent	≥6 months	0.5 mL
Fluzone quadrivalent	6–35 months ≥3 years	0.25 or 0.5 mL* 0.5 mL
Flucelvax quadrivalent	≥6 months	0.5 mL
Flublok quadrivalent	≥18 years	0.5 mL
Fluzone high-dose quadrivalent	≥65 years	0.7 mL
Fluad quadrivalent	≥65 years	0.5 mL

Impact of Flu Vaccination on General Health

The best way to prevent flu and its potentially life-threatening complications is by receiving a yearly flu vaccine (CDC, 2023a). Research shows the positive impact flu vaccines have on the health of the population:

• During seasons when flu vaccines are similar to circulating flu viruses, flu vaccine has been shown to reduce the risk of a doctor visit for flu by 40%–60%.
• Flu vaccination is associated with lower rates of some cardiac events among people with heart disease, especially among those who have had a cardiac event in the past year.
• Vaccination can reduce the risk of flu-related worsening of chronic lung disease requiring hospitalization.
• Among people with diabetes and chronic lung disease, flu vaccination has been shown to be associated with reduced hospitalizations from a worsening of their chronic condition.
• In children ages 6 months to 17 years, vaccination has been found to reduce risk of severe life-threatening hospitalization by 41% and flu-related emergency department visits by half.
  (CDC, 2023c)