Influenza Vaccine

• Inactivated influenza vaccine (IIV)

• Live-attenuated influenza vaccine (LAIV)

Trivalent vaccines are gradually being superseded by quadrivalent vaccines that cover an additional B virus strain. A quadrivalent recombinant influenza vaccine (RIV4) and a cell culture–based vaccine (ccIIV4) that do not contain egg protein are available. High-dose quadrivalent vaccines are available for patients ≥ 65 years of age. (See also CDC: Different Types of Flu Vaccines.)

Annual vaccination against influenza with an age-appropriate formulation is recommended for all people ≥ 6 months of age who do not have a contraindication. (See CDC: Child and Adolescent Immunization Schedule by Age and CDC: Adult Immunization Schedule by Age.)

Inactivated influenza vaccine (IIV) can be given to all people ≥ 6 months, including pregnant women.

Recombinant influenza vaccine (RIV4) can be used in people aged 18 to 49 years.

Live-attenuated influenza vaccine (LAIV) can be given to healthy people aged 2 to 49 years who are not pregnant and who do not have immunocompromising conditions. Safety of LAIV has not been established in people with disorders that predispose them to complications from influenza, including advanced lung disease or asthma.

Adults ≥ 65 years should be given any one of the quadrivalent high-dose IIV, quadrivalent recombinant influenza vaccine, or quadrivalent adjuvanted IIV. If none of these are available, then any other age-appropriate influenza vaccine should be used. The high dose is recommended only for those ≥ 65 years.

Health care workers who care for immunocompromised people (ie, those who require care in a protected environment) should be given IIV or RIV4 rather than LAIV (or they should avoid contact with the immunocompromised people for 7 days after getting the vaccine).

The main contraindication for IIV is

• A severe allergic reaction (eg, anaphylaxis) after previous dose of IIV or to a vaccine component, including egg protein

Precautions with IIV include

• Moderate or severe acute illness with or without fever (vaccination is postponed until illness resolves)

• Guillain-Barré syndrome (GBS) within 6 weeks after a previous dose of an influenza vaccine

Contraindications for LAIV include

• A severe allergic reaction (eg, anaphylaxis) to any vaccine component (excluding egg) or to a previous dose of any influenza vaccine

• Immunocompromise (eg, due to disorders, including HIV infection, or use of immunosuppressants)

• Close contact with and/or caring for severely immunocompromised patients who require a protected environment (unless contact is avoided for 7 days after receiving LAIV)

• Pregnancy

• Anatomical or functional asplenia

• Receipt of influenza antiviral drugs in the past 48 hours

• Cerebrospinal fluid leak or a cochlear implant

• Age < 2 years or ≥ 50 years

• Age 2 to 4 years if children have asthma or have had wheezing or asthma episodes in the past 12 months

Precautions for LAIV include

• Certain chronic disorders such as chronic lung, heart, kidney, liver, hematologic (eg, hemoglobinopathies), or metabolic (eg, diabetes mellitus) disorders

• Asthma in people aged ≥ 5 years

• Moderate or severe acute illness with or without fever (vaccination is postponed until illness resolves)

• Guillain-Barré syndrome within 6 weeks after a previous dose of an influenza vaccine

The main contraindication for RIV4 is

• A severe allergic reaction (eg, anaphylaxis) after a previous dose of RIV4

Precautions with RIV4 include

• Moderate or severe acute illness with or without fever (vaccination is postponed until illness resolves)

• Guillain-Barré syndrome within 6 weeks after a previous dose of an influenza vaccine

Precautions for patients with suspected egg allergy: Patients with a history of egg allergy who have had only hives after exposure to egg should be given the influenza vaccine. Any influenza vaccine that is otherwise recommended based on the recipient’s age and health status can be used.

The influenza vaccine is given yearly.

For IIV, the dose is

• 0.25 mL or 0.50 mL IM (depending on vaccine) for children aged 6 to 35 months

• 0.5 mL IM for people ≥ 3 years

• 0.1 mL for people aged 18 to 64 years, given intradermally

Children age 6 months to 8 years who have received fewer than 2 influenza vaccine doses or whose influenza vaccination history is unknown should receive 2 doses, separated by at least 4 weeks.

The smaller, intradermal dose can be used to conserve vaccine in times of shortage.

For LAIV, the dose is 0.1 mL, sprayed into each nostril (total dose is 0.2 mL).

For RIV4, the dose is 0.5 mL IM.

For IIV, adverse effects are usually limited to mild pain at the injection site. Fever, myalgia, and other systemic effects are relatively uncommon; however, people who have been vaccinated may mistakenly think that the vaccine is causing influenza. Such reactions do not contraindicate future vaccination, which should be encouraged.

Multidose vials contain thimerosal, a mercury-based preservative. Public concerns about a possible link between thimerosal and autism have proved unfounded; however single-dose vials, which are thimerosal-free, are available.

For LAIV, adverse effects are mild; rhinorrhea is the most common, and mild wheezing may occur.

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

1. Advisory Committee on Immunization Practices (ACIP): Influenza ACIP Vaccine Recommendations

2. ACIP: Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the ACIP—United States, 2020–21 Influenza Season

3. ACIP: Recommended Adult Immunization Schedule, United States, 2023 including Changes to the 2023 Adult Immunization Schedule

4. Centers for Disease Control and Prevention (CDC): Influenza Vaccination: Information for Healthcare Professionals

5. European Centre for Disease Prevention and Control (ECDC): Influenza: Recommended vaccinations