Influenza Virus Vaccine (Nasal)

Introduction Overview

Generic Name

influenza virus vaccine (nasal)

Brand Name

FluMist

Dosage Form

nasal spray

Drug Class

Viral vaccines

Pharmacokinetics

Absorption:
FluMist vaccine is administered intranasally, where the live attenuated influenza viruses infect and replicate within the epithelial cells of the nasopharyngeal mucosa. Unlike injectable vaccines, FluMist is not systemically absorbed in measurable quantities, as the vaccine virus remains localized in the upper respiratory tract. This localized replication induces mucosal immune responses involving secretory IgA antibodies. The lack of systemic absorption minimizes systemic exposure and associated systemic side effects.

Distribution:
Since the vaccine is restricted to the nasal mucosa and upper respiratory tract tissues, systemic distribution is negligible. The live attenuated virus is confined primarily to the nasal passages and does not disseminate beyond the site of inoculation. This limited distribution reduces risks of systemic adverse reactions and ensures the immune response is initiated at primary sites of influenza virus entry.

Metabolism:
The live attenuated influenza viruses in FluMist replicate locally within nasal epithelial cells. Following replication, viral particles are cleared by mucociliary mechanisms and immune-mediated processes. The metabolic degradation of viral components occurs via normal cellular pathways within the epithelium and local lymphoid tissue. Since the vaccine virus is attenuated, it is unable to cause productive infection or significant metabolic burden in the host.

Elimination:
Elimination of vaccine viruses predominantly occurs through mucociliary clearance, swallowing, and local immune-mediated destruction. Viral shedding may occur transiently in nasal secretions, primarily within the first few days post-vaccination, but typically does not result in transmission to healthy individuals. The vaccine viruses are ultimately cleared from the respiratory tract without systemic elimination processes.

Clinical Implications:
The intranasal administration route and localized replication optimize mucosal immunity which may provide broader cross-protection. However, because of replication in nasal tissues, individuals with compromised respiratory or immune systems may be at increased risk of adverse effects, necessitating contraindications in such populations.

Dosage Forms

Available Dosage Forms:
-FluMist is exclusively available as a nasal spray. Each single-use device delivers 0.2 mL total (0.1 mL per nostril).

Dosages for Adults and Adolescents:
-For individuals aged 9 through 49 years, the recommended dosage is a single dose administered as one spray in each nostril (0.1 mL per nostril).

Specific Patient Populations:
-For pediatric patients aged 2 through 8 years, dosing involves either a single dose or two doses depending on prior vaccination history, with each dose administered as one spray into each nostril. The second dose, if required, is given at least one month after the first.
-Children under 2 years old are not recommended FluMist due to an increased risk of wheezing.
-Pregnant and breastfeeding women are advised to consult healthcare providers before use; systemic absorption is minimal, but live vaccines are generally avoided.

Clinical Guidelines:
-FluMist vaccine must be refrigerated at 2-8°C and protected from light. The nasal spray device should remain in its carton until use.
-Annual administration is recommended each flu season to match circulating virus strains.
-Administration instructions emphasize rapid, single-motion depression of the plunger into each nostril with the patient upright.
-Sniffing is not required following administration.

Mechanism Of Action

FluMist is a live attenuated influenza vaccine designed to stimulate immunity by mimicking natural infection without causing disease. The vaccine contains weakened influenza virus strains that replicate primarily in the cooler temperatures of the upper respiratory tract, inducing a robust mucosal immune response.

Upon intranasal administration, the live attenuated influenza viruses infect epithelial cells of the nasal mucosa, initiating localized viral replication. This triggers both innate and adaptive immune responses, including the production of secretory IgA antibodies at mucosal surfaces, systemic IgG antibodies, and activation of cell-mediated immunity involving CD4+ and CD8+ T lymphocytes.

This multifaceted immune activation confers protection by neutralizing circulating influenza viruses upon exposure, reducing viral shedding and illness severity. The mechanism contrasts with inactivated influenza vaccines, which primarily induce systemic antibody responses without significant mucosal immunity.

Clinical studies indicate that mucosal immunity elicited by FluMist may provide broader cross-protection against heterologous influenza strains and potentially reduce transmission. However, the need for replication in the nasal mucosa underlies contraindications in individuals with respiratory illnesses or immunocompromised states. The vaccine's efficacy depends on the antigenic match between vaccine strains and circulating influenza viruses, with annual reformulation to address viral antigenic drift.

Pharmacological Actions

Induces active immunity against influenza virus through live attenuated viral replication in nasal mucosa.
Stimulates mucosal secretory IgA production, enhancing protection at virus entry sites.
Elicits systemic humoral immunity with IgG antibodies targeting influenza hemagglutinin and neuraminidase proteins.
Activates cell-mediated immune responses involving T lymphocytes for viral clearance.
Provides prophylactic protection against multiple influenza virus strains including influenza A subtypes (H1N1, H3N2) and influenza B lineages.
Reduces severity and incidence of influenza illness during flu season through immune memory induction.
Potentially decreases viral shedding and influenza virus transmission within communities.
Annual reformulation matches anticipated prevalent influenza strains, ensuring updated antigenic coverage.
Localized replication in nasal epithelium reduces systemic exposure and adverse effect risk compared to inactivated vaccines.
Induces both primary and booster immune responses depending on prior vaccination status and age.

Therapeutic Or Clinical Uses

Prevention of seasonal influenza infection in individuals aged 2 through 49 years.
Indicated for influenza prophylaxis when vaccine strains correspond to circulating influenza viruses.
Suitable for healthy individuals without contraindications to live vaccines.
Used in pediatric populations (2-8 years) with dosing adjusted based on immunization history.
Alternative to injectable influenza vaccines for patients with needle phobia or preference for nasal administration.
Recommended annually to maintain protective immunity against evolving influenza virus strains.
May reduce community transmission of influenza through induction of mucosal immunity.
Prevention of influenza-related complications such as hospitalization and severe respiratory illness.
Used as part of mass immunization strategies during flu seasons to control outbreaks.
May be considered in certain public health vaccination programs depending on age and risk factors.
Administered in outpatient settings including doctor's offices, clinics, and pharmacies.
Repurposed in updated formulations to address emergent influenza variants as per regulatory and CDC guidance.

Side Or Adverse Effects

Common adverse effects include nasal congestion or runny nose in patients aged 2 to 49 years.
Fever exceeding 100°F particularly in children aged 2 through 6 years post-vaccination.
Sore throat reported particularly in adults aged 18 through 49 years.
Mild flu-like symptoms such as headache, muscle aches, chills, fatigue, and irritability.
Low appetite observed occasionally post-vaccination.
Transient wheezing and respiratory distress in children under 2 years, leading to contraindication in this group.
Severe allergic reactions including anaphylaxis, presenting as hives, rash, facial or airway swelling, and breathing difficulties.
Rare but serious hypersensitivity reactions in individuals with egg allergy or vaccine ingredient sensitivity.
Potential transmission of live vaccine virus to severely immunocompromised contacts leading to infection.
Local irritation or discomfort in nasal mucosa post-spray administration.
Possible exacerbation of asthma or reactive airway disease symptoms in susceptible individuals.
Mild systemic symptoms usually resolve spontaneously without intervention.
Incidence of serious adverse events is low but requires monitoring.
Adverse effects tend to occur within days of vaccination and are generally self-limited.
No preservatives included, minimizing risk of preservative-associated adverse reactions.

Precautions

Do not administer to individuals with severe allergy to eggs or any vaccine components.
Avoid use in patients with a history of life-threatening reactions to prior influenza vaccines.
Children and adolescents 2-17 years who take aspirin or salicylates should not receive FluMist due to Reye’s syndrome risk.
Avoid vaccinating children under 2 years old due to risk of wheezing and respiratory complications.
Defer vaccination in patients currently experiencing moderate or severe febrile illness or respiratory infections.
Avoid close contact with immunocompromised individuals for 7 days following vaccination to prevent transmission.
Disclose any history of Guillain-Barré syndrome before administration.
Use caution in patients with underlying chronic conditions such as asthma, heart, kidney, or lung disease, and diabetes.
Pregnant or breastfeeding women should consult healthcare providers before receiving FluMist.
Avoid concurrent use of antiviral influenza medications for at least 2 weeks post-vaccination.
Ensure proper storage and handling to maintain vaccine potency and safety.
Inform healthcare providers about all recent vaccinations prior to administration.
Monitor for allergic reactions during and after vaccination.
Patients should be advised on signs of adverse effects and instructed to seek medical attention if needed.
Inform recipient or guardian about potential mild flu-like symptoms following vaccination.

Warnings

Contraindicated in individuals with severe allergies to eggs or vaccine ingredients.
Should not be given to persons with prior life-threatening reactions to influenza vaccines.
Use is not recommended in children under 2 years due to increased risk of wheezing and respiratory distress.
Avoid use in immunocompromised persons or those living with severely immunocompromised individuals.
Not recommended during pregnancy unless benefits outweigh risks; consult healthcare provider.
Concurrent use of aspirin in children and adolescents 2-17 years increases risk of Reye's syndrome after vaccination.
Avoid initiation or continuation of antiviral influenza drugs within 2 weeks of vaccination, as they may inhibit vaccine virus replication.
Those with current moderate or severe illness should postpone vaccination until recovery.
Immunosuppressive therapies may impair vaccine efficacy and increase risk of adverse reactions.
Potential transmission of vaccine virus to close contacts with weakened immune systems.
Do not use intranasal spray for parenteral administration; designed solely for nasal delivery.
FluMist must not be used beyond the expiration date or if stored improperly.
Monitor for immediate hypersensitivity reactions post-vaccination, especially in history of allergies.
Children with a history of asthma or recurrent wheezing require evaluation prior to vaccine administration.
Rare cases of Guillain-Barré syndrome following influenza vaccination warrant vigilant post-vaccination monitoring.

Contraindication

Severe allergic reaction (e.g., anaphylaxis) to any component of the vaccine including egg protein.
History of life-threatening reaction to any influenza vaccine.
Children under 2 years of age due to risk of respiratory complications.
Use of aspirin or salicylate-containing medications in children and adolescents aged 2 through 17 years.
Individuals with severe immunodeficiency or receiving immunosuppressive therapy.
Current moderate or severe febrile illness or respiratory infection at time of vaccination.
Pregnancy unless benefits outweigh potential risks and advised by healthcare provider.
Previous diagnosis of Guillain-Barré syndrome within 6 weeks following prior influenza vaccination.
Known hypersensitivity to gentamicin or other inactive ingredients in the formulation.
Any condition that contraindicates administration of live attenuated vaccines.
History of severe asthma or active wheezing at time of vaccination.
Close contact with individuals having severe immunosuppression within 7 days post-vaccination.
Concurrent antiviral influenza drugs administration within 48 hours before vaccination.
Use in children less than 24 months due to increased risk of wheezing and hospitalization.
Any other known hypersensitivity to live vaccines.

Drug Interactions

Antiviral influenza medications (amantadine, rimantadine, oseltamivir, zanamivir) may interfere with FluMist live virus replication; avoid use for at least 2 weeks post-vaccination.
Concurrent use of aspirin or salicylate-containing drugs in children and adolescents aged 2-17 increases risk of Reye's syndrome post-vaccination.
Immunosuppressive drugs such as corticosteroids, chemotherapy, or radiation therapy may reduce vaccine effectiveness and increase risk of adverse events.
Interactions with other vaccines require appropriate timing; avoid administering other live vaccines simultaneously without professional guidance.
No significant known interactions with common vitamins and herbal supplements but inform healthcare providers about all supplements used.
Certain immunomodulating agents may alter host immune response to vaccine antigens.
Medications affecting immune system function could blunt the vaccine-induced immune response.
Use of nasal decongestants prior to vaccination may affect vaccine delivery to nasal mucosa.
Nonsteroidal anti-inflammatory drugs (NSAIDs) may mask febrile responses post-vaccination.
No documented interaction with common antibiotics, although immune response may be affected by concurrent infections requiring antimicrobial therapy.
Caution with medications that impair respiratory function in patients receiving FluMist.
Interactions with blood thinners have not been reported but bleeding risk at vaccine site is negligible due to nasal route.
Avoid co-administration with other intranasal medications unless clinically justified and separated by adequate interval.
Drug interaction profiles should be regularly reviewed during vaccination campaigns in polypharmacy patients.
Healthcare providers must assess all concurrent medications prior to FluMist administration.

Preparations Of The Drug

FluMist is provided as a single-dose, prefilled intranasal spray device containing live attenuated influenza virus strains.
Each 0.2 mL spray delivers 0.1 mL into each nostril.
2024-2025 formula contains three live, weakened influenza virus strains: influenza A(H1N1), influenza A(H3N2), and influenza B Victoria lineage.
Inactive ingredients include monosodium glutamate, gelatin, arginine, sucrose, dibasic potassium phosphate, monobasic potassium phosphate, and gentamicin.
Manufactured by MedImmune, LLC, Gaithersburg, MD.
The nasal sprayer device is latex-free and preservative-free.
Must be refrigerated at 2-8°C (35-46°F) and stored in its original carton to protect from light.
Do not use if the product is frozen, expired, or has been stored outside of recommended temperature ranges.
Each device has a dose divider clip that should not be removed prior to administration except as per instructions.
Intended only for intranasal administration; injection or oral use is contraindicated and unsafe.
Vaccine composition is updated annually to reflect influenza virus antigenic changes as recommended by public health authorities.
Supplied in quadrivalent formulations covering multiple influenza virus lineages depending on season.
Sterile, single-use device ensures no need for reconstitution or mixing prior to administration.
Inactivated vaccine alternatives are available for patients unable to receive live attenuated preparations.
Packaging includes detailed administration instructions to ensure correct and safe delivery of the vaccine.