Live Attenuated Influenza Vaccine (LAIV)

Usage

• Medical Conditions: LAIV is prescribed for the active immunization of individuals against influenza caused by virus subtypes A and type B contained in the vaccine. It is specifically indicated for healthy, non-pregnant individuals.
• Pharmacological Classification: Vaccine (viral, live attenuated).
• Mechanism of Action: LAIV introduces weakened live influenza viruses into the nasal passages. These attenuated viruses replicate in the nasopharyngeal mucosa, stimulating a systemic immune response (including humoral and cell-mediated immunity) without causing significant illness. The immune system recognizes the viral antigens, develops antibodies and memory cells, thus providing protection against future infection by similar influenza virus strains.

Alternate Names

• Live Attenuated Influenza Vaccine (LAIV3 for trivalent, LAIV4 for quadrivalent)
• FluMist Quadrivalent (brand name)
• Nasal spray flu vaccine

How It Works

• Pharmacodynamics: LAIV induces both humoral and cell-mediated immunity, similar to natural infection but without causing significant illness. The immune response generated includes the production of antibodies against hemagglutinin (HA) and neuraminidase (NA) surface proteins of the influenza virus, preventing viral attachment and replication. Cell-mediated immunity also plays a role in clearing infected cells.
• Pharmacokinetics: LAIV is administered intranasally, and the attenuated viruses primarily replicate in the nasopharyngeal mucosa. Systemic absorption is limited. The virus does not spread to the lower respiratory tract or other organs. The viruses are eventually cleared by the immune system.
• Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: LAIV’s mechanism of action involves viral replication, antigen presentation, and subsequent immune response. It doesn’t primarily rely on receptor binding, enzyme inhibition, or neurotransmitter modulation like many drugs.
• Elimination Pathways: The attenuated viruses are eliminated by the immune system’s response, including antibody neutralization and cell-mediated cytotoxicity.

Dosage

Standard Dosage

Adults (2 - 49 years old):

• 0.2 mL total, administered as 0.1 mL into each nostril, via intranasal spray.
• Single dose annually, ideally before the onset of influenza activity in the community.

Children (2 - 8 years old):

• 0.2 mL total, administered as 0.1 mL into each nostril, via intranasal spray.
• Two doses, 4 weeks apart, if receiving the flu vaccine for the first time or with unknown vaccination history. Subsequent seasons require a single dose unless other indications emerge (e.g., recent transplant).

Special Cases:

• Elderly Patients (50 years and older): LAIV is not indicated for individuals 50 years and older. Inactivated influenza vaccine (IIV) or recombinant influenza vaccine (RIV) should be used.
• Patients with Renal Impairment: Dose adjustments are not routinely required based on renal impairment.
• Patients with Hepatic Dysfunction: Dose adjustments are not routinely required based on hepatic dysfunction.
• Patients with Comorbid Conditions: LAIV is contraindicated in individuals with specific comorbid conditions. Check the section on contraindications.

Clinical Use Cases

LAIV is indicated solely for pre-season prophylaxis against influenza. It is not relevant in clinical settings such as intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations.

Dosage Adjustments

Dosage adjustments are not routinely made for LAIV based on renal/hepatic dysfunction, metabolic disorders, or genetic polymorphisms. Its limited systemic absorption reduces concerns related to these factors. Consult an allergist if concerns exist.

Side Effects

Common Side Effects:

• Runny nose/nasal congestion
• Wheezing (especially in young children)
• Headache
• Sore throat/cough
• Fever

Rare but Serious Side Effects:

• Severe allergic reaction (anaphylaxis)

Long-Term Effects:

No significant long-term side effects have been associated with LAIV.

Adverse Drug Reactions (ADR):

• Anaphylaxis (rare). Requires immediate medical intervention.

Contraindications

• History of severe allergic reaction to any vaccine component (including egg protein, gelatin, or gentamicin) or a previous dose of any influenza vaccine.
• Age under 2 years or over 49 years.
• Pregnancy.
• Immunocompromised state (e.g., HIV infection, cancer treatment, immunosuppressive medications).
• Children/adolescents receiving aspirin or salicylate therapy (due to the risk of Reye’s syndrome).
• Close contact with severely immunocompromised individuals requiring a protected environment (unless contact can be avoided for 7 days post-vaccination).
• Anatomical or functional asplenia.
• Cranial cerebrospinal fluid (CSF) leaks or cochlear implant.
• Severe asthma or recent wheezing.

Drug Interactions

• Influenza Antiviral Medications: LAIV should not be administered until 48 hours after discontinuing influenza antivirals (oseltamivir, zanamivir). Antivirals should not be started until 2 weeks after LAIV administration unless medically necessary. If given concomitantly, consider revaccination later.
• Aspirin/Salicylates: Contraindicated in children/adolescents due to risk of Reye’s syndrome. Avoid aspirin-containing products for 4 weeks after LAIV unless medically necessary.

Pregnancy and Breastfeeding

• Pregnancy: LAIV is contraindicated in pregnancy. Inactivated or recombinant influenza vaccines are preferred during pregnancy.
• Breastfeeding: Inactivated or recombinant influenza vaccines are preferred during breastfeeding. LAIV may be considered if other influenza vaccines are unavailable and the benefit outweighs any theoretical risk.

Drug Profile Summary

• Mechanism of Action: Induces immunity through replication of attenuated influenza viruses in the nasopharynx.
• Side Effects: Commonly runny nose, nasal congestion, headache, sore throat, cough, fever. Rarely, anaphylaxis.
• Contraindications: Pregnancy, immunocompromise, age under 2 or over 49, severe asthma, allergy to vaccine components.
• Drug Interactions: Influenza antivirals, aspirin/salicylates.
• Pregnancy & Breastfeeding: Contraindicated in pregnancy. Alternatives preferred during breastfeeding.
• Dosage: 0.2 mL intranasally, single dose annually (2 doses, 4 weeks apart, for children 2-8 years old receiving the vaccine for the first time).
• Monitoring Parameters: Primarily monitor for allergic reactions. If respiratory symptoms develop, evaluate to rule out true influenza infection.

Popular Combinations

LAIV is not generally combined with other vaccines in the same syringe or administered as a mixed formulation. However, it can be given concomitantly with other inactivated vaccines. If other live vaccines are indicated, separate administration by at least 28 days.

Precautions

• General Precautions: Screen for contraindications, including allergy history, immune status, and current medications.
• Specific Populations (see contraindications and pregnancy/breastfeeding sections for details).
• Lifestyle Considerations: No specific lifestyle restrictions are associated with LAIV.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Live Attenuated Influenza Vaccine?

A: Adults and children 2-49 years old: 0.2 mL intranasally (0.1 mL in each nostril). Children 2-8 years old receiving the vaccine for the first time need two doses, 4 weeks apart.

Q2: Who should not receive LAIV?

A: Pregnant women, individuals with severe egg allergy, immunocompromised persons, children under 2 years or adults over 49, and those with certain chronic conditions (e.g., severe asthma).

Q3: Can LAIV be given with other vaccines?

A: Yes, LAIV can be given concomitantly with other inactivated vaccines. Separate administration by at least 28 days if other live vaccines are given.

Q4: What are the most common side effects of LAIV?

A: Runny nose, nasal congestion, headache, sore throat, cough, and low-grade fever.

Q5: Can LAIV give someone the flu?

A: No. LAIV contains attenuated (weakened) viruses that cannot cause influenza. Mild symptoms similar to a cold may occur.

Q6: How is LAIV administered?

A: Intranasally, using the prefilled sprayer provided. 0.1 mL is sprayed into each nostril.

Q7: When should LAIV be administered?

A: Ideally before the onset of influenza activity in the community, typically September or October. Vaccination may be offered as long as the circulating strains match the vaccine components.

Q8: Who should receive two doses of LAIV?

A: Children aged 2-8 years who are receiving the flu vaccine for the first time or if their prior vaccination status is unknown.

Q9: What should I do if a patient experiences an allergic reaction to LAIV?

A: Immediately administer epinephrine and provide supportive care as needed.

Q10: How long does the protection from LAIV last?

A: Protection may diminish over time. Annual vaccination is recommended to ensure optimal protection against currently circulating influenza strains.