Inactivated influenza vaccine

Usage

• Medical Conditions: Inactivated influenza vaccines (IIV, IIV3, IIV4, HD-IIV3, HD-IIV4, ccIIV3, ccIIV4, RIV3, RIV4, aIIV3, aIIV4) are prescribed for the prevention of influenza (flu) infection.
• Pharmacological Classification: Vaccine.
• Mechanism of Action: These vaccines contain inactivated (killed) influenza viruses. They work by exposing the body to small amounts of inactivated viral antigens (hemagglutinin and neuraminidase), stimulating the immune system to produce antibodies. These antibodies then provide protection against future infection with the same or similar strains of influenza virus.

Alternate Names

• Flu shot

• Flu vaccine (inactivated)

• Trivalent influenza vaccine (IIV3)

• Quadrivalent influenza vaccine (IIV4)

• High-dose trivalent influenza vaccine (HD-IIV3)

• High-dose quadrivalent influenza vaccine (HD-IIV4)

• Cell-culture based IIV3/IIV4

• Recombinant influenza vaccine (RIV3/RIV4)

• Adjuvanted IIV3/IIV4

• Brand names: Fluzone, Fluarix, FluLaval, FluMist (note, FluMist is a live attenuated vaccine), Flucelvax, Flublok, Fluad, Afluria.

How It Works

• Pharmacodynamics: The inactivated influenza vaccine stimulates the immune system, specifically humoral immunity, producing antibodies targeting the hemagglutinin and neuraminidase surface proteins of the influenza virus. The antibodies bind to the virus and neutralize it, hence preventing its entry into the body’s cells.
• Pharmacokinetics: The vaccine is administered intramuscularly (IM) or intradermally (ID), the antigens are processed by antigen-presenting cells, and an immune response is initiated. Antibody titers typically peak within 2 weeks of vaccination. Data on the specific metabolism and elimination of inactivated influenza virus antigens are limited.
• Mode of Action/Receptor binding, enzyme inhibition, or neurotransmitter modulation: The inactivated virus particles do not replicate or cause infection. The hemagglutinin and neuraminidase antigens are recognized by the immune system as foreign, triggering B cells to differentiate into antibody-producing plasma cells. The primary mechanism is antibody-mediated neutralization.
• Elimination Pathways: Specific data on the elimination pathways of inactivated viral antigens are not readily available.

Dosage

Standard Dosage

Adults:

• 0.5 mL IM, annually. Adults 65 years and older should preferentially receive HD-IIV3, RIV3, aIIV3, or aIIV4.
• HD-IIV3/HD-IIV4, RIV3/RIV4, aIIV3/aIIV4: 0.5 mL IM annually, preferentially for adults 65 years and older.
• ID Fluzone Intradermal Quadrivalent (for ages 18-64): 0.1ml intradermally.

Children:

• 6-35 months:
  • Fluzone, Afluria: 0.25 mL or 0.5 mL IM.
  • Fluarix, FluLaval, Flucelvax: 0.5 mL IM.
• 3-17 years: 0.5 mL IM
• Children aged 6 months through 8 years receiving influenza vaccine for the first time: Two doses (0.25ml or 0.5ml, depending on product and age), administered at least 4 weeks apart.
• If a child turns 9 years of age between doses, the second dose should still be administered.
• A second dose is needed for a 9-year-old child who received one dose in the current season while they were age 8 years, if they have not or don’t know if they have received 2 doses in prior years.

Special Cases:

• Elderly Patients (65 years and older): Preferentially HD-IIV, RIV, or aIIV, 0.5ml IM dose. If none are available, any age-appropriate IIV or RIV may be used.
• Patients with Renal Impairment: Dose adjustments are not typically necessary.
• Patients with Hepatic Dysfunction: Dose adjustments are not typically necessary.
• Patients with Comorbid Conditions: Standard dosing is generally appropriate, but certain conditions may influence vaccine choice (e.g. immunocompromised patients). Live, attenuated influenza vaccine (LAIV) is contraindicated in some patients with chronic medical conditions.

Clinical Use Cases These vaccines are for the prevention of influenza, not treatment or emergency use, and hence are not indicated in the following scenarios.

• Intubation
• Surgical Procedures
• Mechanical Ventilation
• Intensive Care Unit (ICU) Use
• Emergency Situations

Dosage Adjustments Standard dosing is generally appropriate unless otherwise stated.

Side Effects

Common Side Effects:

• Injection site reactions (soreness, redness, swelling)
• Headache
• Myalgia
• Fatigue
• Fever
• Chills

Rare but Serious Side Effects:

• Allergic reactions, including anaphylaxis (rare)
• Guillain-Barré Syndrome (GBS) (very rare)

Long-Term Effects: No significant long-term adverse effects are associated with inactivated influenza vaccines.

Contraindications:

• Severe allergic reaction (e.g., anaphylaxis) to a previous dose of any influenza vaccine or to any vaccine component (excluding egg protein for most vaccines).
• History of GBS within 6 weeks of a previous influenza vaccination, with no other identified cause.

Drug Interactions:

• Immunosuppressant medications: may reduce immune response to vaccine
• Antiviral medications (e.g., oseltamivir, zanamivir): Administer LAIV 2 weeks before or 48 hours after the antiviral medications. Administer LAIV 17 days before or 2 weeks after baloxavir and 5 days before or 2 weeks after peramivir.
• Aspirin and salicylates: Not recommended for children/adolescents for 4 weeks after vaccination due to risk of Reye’s syndrome.

Pregnancy and Breastfeeding:

• Pregnancy: Recommended during any trimester.
• Breastfeeding: Generally considered safe. Antibodies generated by the mother can be passed to the infant through breast milk, providing potential passive immunity.

Drug Profile Summary

• Mechanism of Action: Stimulates antibody production against influenza virus antigens.
• Side Effects: Injection site reactions, headache, myalgia, fever, chills. Rarely, allergic reactions or GBS.
• Contraindications: Severe allergic reaction to a previous dose or vaccine component (excluding egg for most vaccines), history of GBS.
• Drug Interactions: Immunosuppressants, antivirals, aspirin/salicylates (in children/adolescents).
• Pregnancy & Breastfeeding: Recommended during pregnancy and breastfeeding.
• Dosage: 0.5 mL IM for most adults and children over 3 years. Dosage and schedule may differ for young children and certain vaccines. See above sections for specifics.
• Monitoring Parameters: Monitor for signs of allergic reaction and GBS.

Popular Combinations: Often given with other vaccines.

• Pneumococcal vaccine

Precautions:

• General Precautions: Pre-screening for allergies and contraindications.
• Pregnant Women: Recommended during any trimester.
• Breastfeeding Mothers: Safe to breastfeed after receiving the vaccine.
• Children & Elderly: Age-specific dosing adjustments are necessary.
• Lifestyle Considerations: No specific lifestyle considerations.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Inactivated influenza vaccine?

A: See the Dosage section above for detailed recommendations.

Q2: Can pregnant women receive the inactivated influenza vaccine?

A: Yes, it is recommended for pregnant women during any trimester.

Q3: What are the common side effects of the inactivated influenza vaccine?

A: Common side effects include injection site reactions (pain, redness, swelling), headache, muscle aches, fatigue, fever, and chills.

Q4: Are there any contraindications to receiving the inactivated influenza vaccine?

A: Yes, contraindications include a history of severe allergic reaction to a previous dose of any influenza vaccine or any vaccine component (other than egg protein for most vaccines), and history of Guillain-Barré Syndrome (GBS) within 6 weeks of a previous influenza vaccination (with no other identified cause).

Q5: Can I get the flu from the inactivated influenza vaccine?

A: No, the inactivated influenza vaccine contains killed virus and cannot cause influenza.

Q6: How effective is the inactivated influenza vaccine?

A: Effectiveness varies from season to season depending on the match between the vaccine strains and circulating strains, and other factors including recipient age and health.

Q7: Who should receive the high-dose influenza vaccine?

A: Adults aged 65 years and older are preferentially recommended to receive high-dose inactivated influenza vaccine (HD-IIV), recombinant influenza vaccine (RIV), or adjuvanted inactivated influenza vaccine (aIIV). Any other age-appropriate vaccine may be used if these aren’t available.

Q8: Can the inactivated influenza vaccine be given with other vaccines?

A: Yes, it can generally be given at the same time as other vaccines, though different limbs should be used if co-administering with other vaccines that might be more likely to cause a local reaction.

Q9: If a patient has an egg allergy, can they receive the flu vaccine?

A: Yes, for the 2024-2025 influenza season, patients with an egg allergy of any severity can receive any licensed, age-appropriate influenza vaccine.