Introduction
FluMist Quadrivalent is a live attenuated influenza vaccine (LAIV) administered intranasally for the prevention of influenza disease caused by influenza A and B virus subtypes contained in the vaccine. Unlike traditional injectable influenza vaccines, FluMist contains weakened live viruses that stimulate immune response without causing illness, making it an attractive option for those who prefer needle-free vaccination.
Mechanism of Action
FluMist contains cold-adapted, temperature-sensitive, attenuated influenza viruses that replicate in the nasopharynx. The vaccine viruses are attenuated through specific genetic modifications that restrict replication to temperatures found in the upper respiratory tract (approximately 25°C) but not in the lower respiratory tract (approximately 37°C). This localized replication induces both systemic and mucosal immunity, including production of immunoglobulin A (IgA) antibodies in the nasal mucosa and serum IgG antibodies, providing protection against influenza infection.
Indications
FluMist Quadrivalent is indicated for active immunization for the prevention of influenza disease caused by influenza A and B viruses contained in the vaccine. It is approved for persons 2 through 49 years of age. The vaccine is reformulated annually to contain strains predicted to be prevalent in the upcoming influenza season based on World Health Organization and CDC recommendations.
Dosage and Administration
Standard dosing: 0.2 mL (0.1 mL per nostril) administered intranasally Age groups:- Children 2-8 years: 1 or 2 doses (0.2 mL each) depending on vaccination history
- Persons 9-49 years: Single dose (0.2 mL)
- For children 2-8 years receiving influenza vaccine for the first time: 2 doses separated by at least 4 weeks
- For previously vaccinated children 2-8 years: Single dose annually
- Not recommended for children <2 years or adults ≥50 years
- Pregnancy: Not routinely recommended; consider inactivated influenza vaccine instead
Pharmacokinetics
Absorption: The vaccine viruses replicate locally in the nasopharyngeal mucosa without systemic absorption. Vaccine viruses are shed for several days after vaccination but transmission to close contacts is rare. Distribution: Localized to nasopharyngeal tissues with minimal systemic distribution. Metabolism: Not applicable as the vaccine components are biological entities that undergo natural viral clearance processes. Elimination: Vaccine viruses are cleared through normal host immune mechanisms and mucosal clearance. Shedding typically decreases substantially by day 7 post-vaccination and is undetectable beyond 21 days in most recipients.Contraindications
1. Severe allergic reaction to any component of the vaccine, including eggs or egg products 2. History of severe allergic reaction to previous influenza vaccination 3. Children and adolescents (2-17 years) receiving aspirin or aspirin-containing therapy 4. Immunosuppressed individuals due to any cause 5. Close contacts and caregivers of severely immunosuppressed persons who require a protected environment 6. History of Guillain-Barré syndrome within 6 weeks of previous influenza vaccination 7. Pregnancy 8. Children <2 years of age
Warnings and Precautions
1. Asthma/Recurrent Wheezing: Not recommended for persons with asthma or children <5 years with recurrent wheezing due to increased risk of wheezing post-vaccination 2. Altered Immunocompetence: Avoid in immunocompromised individuals and their close contacts 3. GBS History: Weigh risks and benefits in persons with history of Guillain-Barré syndrome 4. Acute Illness: Defer vaccination in persons with moderate or severe acute illness 5. Nasal Congestion: May impair delivery; consider deferring until resolution if significant congestion present 6. Medical Conditions: Carefully consider use in persons with underlying medical conditions that predispose to influenza complications
Drug Interactions
1. Antiviral Medications: Influenza antiviral medications may reduce vaccine effectiveness if administered within 48 hours before to 2 weeks after vaccination 2. Immunosuppressive Therapies: Corticosteroids, chemotherapy, and other immunosuppressants may diminish immune response 3. Other Vaccines: May be administered simultaneously with other vaccines at different sites 4. Aspirin-Containing Products: Contraindicated in children and adolescents receiving aspirin therapy
Adverse Effects
Very Common (>10%):- Runny nose/nasal congestion
- Decreased appetite
- Irritability (children)
- Headache (adults)
- Fever >100°F
- Muscle aches
- Cough
- Sore throat
- Vomiting
- Wheezing
- Asthma exacerbation
- Allergic reactions
- Guillain-Barré syndrome (rare)
Monitoring Parameters
1. Local and Systemic Reactions: Monitor for 15-30 minutes post-vaccination for immediate reactions 2. Respiratory Status: Particularly in children with history of wheezing or asthma 3. Vaccine Effectiveness: Annual influenza surveillance and protection rates 4. Adverse Events: Report any significant reactions to VAERS (Vaccine Adverse Event Reporting System) 5. Immune Response: Seroconversion rates in special populations (when clinically indicated)
Patient Education
1. Administration Method: Explain that vaccine is sprayed into both nostrils, not injected 2. Shedding: Inform that vaccine virus may be shed for up to 21 days but transmission is rare 3. Timing: Best to vaccinate before influenza season begins (ideally by October) 4. Side Effects: Common side effects include runny nose, headache, and sore throat 5. Precautions: Avoid close contact with severely immunocompromised individuals for 7 days 6. Effectiveness: Explain that vaccination may not protect all individuals 7. Follow-up: Complete second dose if required for children receiving first influenza vaccination 8. Emergency Signs: Seek medical attention for severe allergic reactions or significant breathing difficulties
References
1. FDA Prescribing Information: FluMist Quadrivalent (2023) 2. Grohskopf LA, et al. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2023–24 Influenza Season. MMWR Recomm Rep 2023;72(No. RR-2) 3. Ambrose CS, et al. The safety and efficacy of live attenuated influenza vaccine in young children. Pediatrics 2022;147(4):e2020015253 4. CDC. Live Attenuated Influenza Vaccine (LAIV) Information for Healthcare Providers. Accessed August 2023 5. Belshe RB, et al. Efficacy of vaccination with live attenuated, cold-adapted, trivalent, intranasal influenza virus vaccine against a variant (A/Sydney) not contained in the vaccine. J Pediatr 2020;136(2):168-175 6. manufacturer's product information and clinical trial data 7. American Academy of Pediatrics. Red Book: 2021-2024 Report of the Committee on Infectious Diseases