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Mechanism of Action
US Drug Names
Not recommended at this time; further safety and efficacy data are needed. The effectiveness of the vaccine was not demonstrated in a trial of 641 patients 50 to 64 years of age. NOTE: If indicated, these patients should receive the annual injectable flu vaccine. Since elderly patients are considered a 'high-risk' group for influenza, vaccination with the injectable form is important for this age group.
0.2 mL/dose intranasally (0.1 mL into each nostril, for a total of 0.2 mL).
0.2 mL/dose intranasally (0.1 mL into each nostril, for a total of 0.2 mL). Repeat the dose at least 4 weeks later for those who are receiving the flu vaccine for the first time. The Advisory Committee on Immunization Practices (ACIP) recommends that infants and children aged 6 months through 8 years who have previously received at least 2 doses of trivalent or quadrivalent influenza vaccine before the beginning of the influenza season, receive only 1 dose for the current season. The 2 previous doses need not have been given during the same season or consecutive seasons.
< 50 years: 0.2 mL/dose intranasally.
>= 50 years: Safety and efficacy have not been established.
Safety and efficacy have not been established.
0.2 ml/dose intranasally.
>= 2 years: 0.2 mL/dose intranasally.
< 2 years: Safety and efficacy have not been established.
Specific guidelines for dosage adjustments in hepatic impairment are not available; it appears that no dosage adjustments are needed.
Specific guidelines for dosage adjustments in renal impairment are not available; it appears that no dosage adjustments are needed.
NOTE: The 2020/2021 trivalent vaccine virus strains for egg-based vaccines are an A/Guangdong-Maonan/SWL1536/2019 (H1N1) pdm09-like virus, an A/HongKong/2671/2019 (H3N2)-like virus, and a B/Washington/02/2019-like virus (B/Victoria lineage). In addition to these virus strains, the 2020/2021 quadrivalent virus vaccine contains a B/Phuket/3073/2013-like virus (B/Yamagata lineage).
Quadrivalent live-attenuated influenza vaccine (LAIV4) is a liquid, cold-adapted vaccine containing live-attenuated influenza viruses that are administered as a nasal spray. Intranasal administration stimulates localized mucosal antibody formation, and because the vaccine contains attenuated viruses, an adjuvant to enhance antigen immunogenicity is not needed. The Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics (AAP) recommends annual flu vaccination with an age-appropriate influenza vaccine (i.e., inactivated influenza vaccine (IIV), quadrivalent recombinant influenza vaccine (RIV4), or LAIV4), without preference of 1 product or formulation over another, for everyone 6 months and older.   The LAIV4 may not be appropriate for patients with immunosuppression. The IIV is preferred over the LAIV4 for vaccinating household members, health-care workers, and others who have close contact with severely immunosuppressed persons during periods when such persons require care in a protected environment. The duration of influenza vaccine virus replication and shedding after LAIV4 administration is unknown. As a precautionary measure, recipients of LAIV4 should avoid close contact with severely immunosuppressed persons for 7 days after vaccination. 
Updates for coronavirus disease 2019 (COVID-19):
The 2020-21 influenza season will coincide with the continued or recurrent circulation of SARS-CoV-2. Influenza vaccination of patients 6 months and older may reduce symptoms that might be confused with those of COVID-19. Additionally, prevention and reduction of influenza severity could decrease hospitalizations and intensive care unit admissions and alleviate stress on the health care system.
For storage information, see the specific product information within the How Supplied section.
Adverse reactions associated with administration of the intranasal influenza vaccine are usually mild. Adverse reactions in adults and children include nasal congestion (9% to 58%), rhinorrhea (44% to 58%), sneezing (2%), sore throat (5% to 28%), irritability (12% to 21%), headache (3% to 40%), lethargy (6% to 14%), weakness (26%), sinusitis (4%), fever (more than 100 degrees F, (7% to 16%), myalgia (2% to 17%), anorexia (13% to 21%), abdominal pain (2% to 12%), chills (2% to 9%), and cough (14%). More patients who received the vaccine than those who received placebo had otitis media (3% vs. 1%, respectively). Asthma attacks or wheezing symptoms have been reported. Rarely, immediate allergic reactions occur after influenza vaccination in all populations. An allergic reaction may present as urticaria, rash, angioedema, bronchospasm, and/or anaphylactic shock; these reactions are most likely the result of hypersensitivity to residual egg protein. Postmarketing, hypersensitivity reactions including anaphylactoid reactions, facial edema, and urticaria have been reported. Pericarditis, meningitis, eosinophilic meningitis, vaccine-associated encephalitis, nausea, vomiting, and diarrhea have also been reported postmarketing. 
No cases of Guillain-Barre syndrome (GBS) have been reported with the intranasal influenza vaccine. However, an increased risk of developing GBS after administration of the inactivated influenza virus vaccine was evident in 1976. Subsequent influenza vaccinations during the next few years were not associated with this increased risk. However, during 1993 to 94 twice the average yearly rate (for the period 1990 to 95) of influenza vaccine-associated incidences of GBS were reported, representing a risk of slightly more than 1 additional case of GBS per million persons vaccinated. In most cases, symptoms were limited and reversible, but fatalities have occurred. Persons with a history of GBS have a substantially greater likelihood of subsequently developing GBS than persons without such a history. Thus, the likelihood of coincidentally developing GBS after influenza vaccination is expected to be greater among persons with a history of GBS than among persons with no history of this syndrome. It is not known if influenza vaccination is causally associated with this risk for recurrence of GBS. 
Prior to administration, inform the patient, parent, guardian, or responsible adult of the benefits and risks of the vaccine, and provide the Vaccine Information Statement, accessible at the Centers for Disease Control and Prevention (CDC) website. These actions are required by the National Childhood Vaccine Injury Act of 1986. If a dose of influenza vaccine has been previously given, question the patient, parent, or guardian about previous adverse reactions that may preclude further administration. Report all adverse reactions to the Vaccine Adverse Event Reporting System (VAERS), as well as the manufacturer. The toll-free number for VAERS is 1-800-822-7967. Educate the responsible adult(s) to promptly report any adverse reaction after vaccine administration to a health care provider.
The decision to administer or to delay vaccination with the intranasal influenza virus vaccine because of current febrile illness depends on the severity of symptoms and the etiology of the disease. The Advisory Committee on Immunization Practices recommends that vaccinations be delayed during a moderate or severe acute febrile illness unless the patient is at immediate risk of infection; administer the vaccine as soon as possible after the acute phase of illness has resolved. All vaccines can be administered to persons with minor illnesses such as diarrhea, mild upper-respiratory infection with or without low-grade fever, or other low-grade febrile illness. However, if nasal congestion is present that might impede delivery of the vaccine to the nasopharyngeal mucosa, then administration of the intranasal vaccine should be deferred until the congestion has resolved or the inactivated influenza vaccine should be used. Allergic rhinitis does not preclude intranasal influenza vaccine administration. There are no data regarding concurrent intranasal corticosteroid administration and the use of intranasal influenza vaccine.
The live-attenuated influenza vaccine (LAIV4) is contraindicated in individuals with a known history of a severe allergic reaction (e.g., anaphylaxis) to the vaccine or any of its components or persons who have had life-threatening reactions to any previous influenza vaccination. The FDA-approved product labeling states that LAIV4 is also contraindicated in patients with egg hypersensitivity because these vaccines are prepared using embryonated chicken eggs. The Advisory Committee on Immunization Practices (ACIP) recommends administering any licensed, age-appropriate influenza vaccine (i.e., inactivated influenza vaccine (IIV), quadrivalent recombinant influenza vaccine (RIV4), or LAIV4) to patients with egg allergy of any severity. Patients who have had symptoms other than urticaria after egg exposure (i.e., angioedema, respiratory distress, lightheadedness, or recurrent emesis) or required emergency medical intervention, may also receive any licensed, age-appropriate influenza vaccine; however, it is recommended that the vaccine only be administered in an inpatient or outpatient medical setting by a health care provider experienced in the recognition and management of severe allergic conditions. Severe allergic reactions to vaccines can occur in patients without a history of previous allergic reaction. A previous severe allergic reaction to influenza vaccine is a contraindication to receiving future influenza vaccines. Although no specific observation time is recommended for egg-allergic patients, ACIP recommends patients be observed for syncope for 15 minutes after vaccination.  The American Academy of Pediatrics (AAP), the American Academy of Allergy, Asthma, and Immunology (AAAAI), and the American College of Allergy, Asthma, and Immunology (ACAAI) do not recommend any special precautions for egg-allergic recipients, regardless of severity. The AAAAI and ACAAI consider any special precautions (i.e., special observation periods or administration in a specialized medical setting) unnecessary due to the extremely rare risk of anaphylactic reactions after vaccination. They recommend that providers and screening questionnaires not ask about the egg allergy status of the influenza virus vaccine recipient.  Each 0.2 mL LAIV4 dose contains 2 mg/dose hydrolyzed porcine gelatin, 2.42 mg/dose arginine, and less than 0.015 mcg/mL gentamicin sulfate. Patients with gelatin hypersensitivity, arginine hypersensitivity, or aminoglycoside hypersensitivity may be inappropriate candidates for LAIV4 receipt. As with any biologic product, the prescriber or health care professional should have procedures in place to manage allergic reactions. The health care professional should have immediate availability of epinephrine (1 mg/mL) injection and other agents used in the treatment of severe anaphylaxis in the event of a serious allergic reaction to the intranasal influenza vaccine.
The intranasal influenza vaccine is not absorbed systemically after intranasal administration and use during pregnancy is not expected to result in fetal exposure to the drug. However, adequate and well-controlled studies have not been conducted in pregnant women and the ability of the vaccine to cause fetal harm or affect reproductive capacity is unknown. During animal studies, no evidence of impaired fertility or fetal harm was noted with intranasal influenza vaccine. According to the Advisory Committee on Immunization Practices (ACIP), administration of live vaccines to pregnant women should be avoided. However, because pregnancy may increase the risk of serious medical complications from influenza, the ACIP recommends that all women who are pregnant or will be pregnant (in any trimester) during influenza season be routinely vaccinated with an inactivated influenza virus vaccine.
According to the CDC, live-virus vaccines administered to a lactating woman do not affect the safety of breast-feeding for women or their infants. Although live viruses in vaccines can replicate in vaccine recipients (i.e., the mother), the majority of live viruses in vaccines have been demonstrated not to be excreted in human milk. If infection does occur, it is well tolerated because the virus is attenuated. There are no data to suggest that passive transfer of antibodies in human milk can affect the efficacy of live-virus vaccines. Breastfed infants should be vaccinated according to the recommended schedule. The manufacturer recommends caution when administering to nursing mothers. Consider the benefits of breast-feeding, the risk of potential infant drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding infant experiences an adverse effect related to a maternally administered drug, health care providers are encouraged to report the adverse effect to the FDA.
The intranasal influenza vaccine is a live vaccine, and live vaccines are contraindicated in patients with severe combined immunodeficiency (SCID). The intranasal influenza vaccine has not been evaluated in patients with other forms of immunosuppression (i.e., IgA deficiency, hypogammaglobulinemia, agammaglobulinemia, or dysgammaglobulinemia) and use in these patients is not recommended. The vaccine should not be used in patients with anatomical or functional asplenia, anyone with cranial cerebrospinal fluid leak, or cochlear implant. Patients with cochlear implants are at risk for cerebrospinal (CSF) leak for a period after implantation. The intranasal influenza vaccine should also not be administered to those with cellular immune deficiency or those patients on immunosuppressive therapy such as high-dose corticosteroid therapy. However, corticosteroid therapy usually is not a contraindication to administering live-virus vaccines when administration is short-term (less than 2 weeks); a low-to-moderate dose (less than 2 mg/kg of body weight or 20 mg/day of prednisone or equivalent for persons who weigh more than 10 kg when administered for less than 2 weeks); long-term, alternate-day treatment with short-acting preparations; maintenance physiologic doses (replacement therapy); or when administered topically (skin, eyes), inhaled, or by local injection. Healthcare providers should wait at least 1 month after discontinuation of high-dose corticosteroid therapy given for more than 2 weeks before administering the intranasal influenza vaccine.   
The live-attenuated influenza vaccine (LAIV4) is not the preferred agent for use in patients with a history of asthma or reactive airway disease, particularly pediatric patients younger than 5 years old with recurrent wheezing, due to the increased risk of wheezing after administration; weigh the potential benefit against the potential risk. In a placebo-controlled safety study, an increase in asthma events was observed among patients younger than 5 years of age. Do not administer LAIV4 to patients with severe asthma or active wheezing because these individuals have not been studied in clinical trials. The inactivated influenza virus vaccine is the recommended product for patients with asthma or a history of wheezing in the past 12 months (for pediatric patients ages 2 to younger than 5 years).
The live-attenuated influenza vaccine is not indicated for use in geriatric patients; the vaccine is only indicated for patients 2 to 49 years of age. The effectiveness of the vaccine was not demonstrated in a clinical trial with a subgroup of patients 50 to 64 years of age.
Neonates, infants, and children younger than 2 years of age should not receive the quadrivalent live-attenuated influenza vaccine (LAIV4). In clinical trials, an increased risk of wheezing, that required bronchodilator therapy or was associated with significant respiratory symptoms within 6 weeks of vaccination, and hospitalization (for any cause within 6 months) was observed among pediatric patients younger than 2 years who received LAIV4 (5.9% and 4.2%, respectively) compared with those who received inactivated influenza vaccine (3.8% and 3.2%, respectively). The inactivated influenza virus vaccine should be used to vaccinate infants and children 6 months to 2 years of age. In addition, children younger than 5 years of age with recurrent wheezing may be at increased risk for wheezing after administration of the intranasal influenza vaccine. LAIV4 is contraindicated in children and adolescents up to 17 years of age receiving salicylate therapy (e.g., aspirin or aspirin-containing therapy). The intranasal influenza vaccine is a live vaccine, and thus could potentially result in influenza infection and in the development of Reye's syndrome in these patients.
Carefully consider the potential benefits and risks of the live-attenuated influenza vaccine (LAIV4) for patients who have developed Guillain-Barre syndrome (GBS) within 6 weeks of a previous influenza vaccination. Persons with a history of GBS have a substantially greater likelihood of subsequently developing GBS than persons without such a history. It is not known whether influenza vaccination is causally associated with this risk for recurrence of GBS. Nevertheless, as a precaution, the ACIP generally recommends against influenza immunization in patients who have developed GBS within 6 weeks of a previous influenza vaccination. However, for most persons with a history of GBS who are at high risk for severe complications from influenza, many experts believe the benefits of the influenza virus vaccine justify yearly vaccination.
The safety of the quadrivalent live-attenuated influenza vaccine (LAIV4) in individuals with underlying medical conditions that may predispose them to complications after wild-type influenza infection (e.g., chronic pulmonary, including chronic obstructive pulmonary disease (COPD), cardiovascular, renal, metabolic, neurologic, hematologic, or hepatic disease) has not been established; only administer the LAIV4 if the potential benefit outweighs the potential risk.  The American Academy of Pediatrics specifically recommends the use of the inactivated influenza virus vaccine for all pediatric patients with the following conditions: asthma; chronic pulmonary diseases, including chronic lung disease (CLD) and cystic fibrosis; hemodynamically significant cardiac disease; immunosuppressive disorders, including HIV infection; sickle cell disease or other hemoglobinopathy; chronic renal dysfunction (e.g., renal failure); chronic metabolic disease (e.g., diabetes mellitus); conditions that require long-term aspirin therapy, such as juvenile idiopathic arthritis or Kawasaki disease; and any condition that can compromise respiratory function or handling of secretions (e.g., neuromuscular disease such as multiple sclerosis, seizure disorder, spinal cord injuries, neurodevelopmental disorders).
The efficacy of the intranasal influenza vaccine has not been established in patients with human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS). The guidelines for the prevention and treatment of opportunistic infections in adults and adolescents with HIV considers use of the live attenuated influenza vaccine (LAIV) administered via the nasal route as contraindicated in patients with HIV. The live virus vaccine theoretically could cause serious influenza infection in these patients. However, among 28 adult patients with HIV infection (median CD4 count of 541 cells/mm3), no serious adverse reactions were reported during the 4 weeks after vaccine receipt. Vaccine strain (type B) virus was detected in 1 of 28 HIV-infected subjects on Day 5 only. The CDC recommends immunization of HIV-infected individuals with the inactivated influenza vaccine, as this measure is safe and may confer protection against influenza. 
The intranasal influenza vaccine is not recommended in patients with neoplastic disease that causes bone marrow suppression or affects the lymphatic system such as leukemia or lymphoma, including patients currently receiving chemotherapy or radiation therapy. Patients with leukemia, lymphoma, or other malignancies whose disease is in remission and whose chemotherapy or radiation therapy has been terminated for at least 3 months can receive live-virus vaccines. The intranasal influenza vaccine is also not recommended for close contacts of severely immunosuppressed persons who require a protected environment. 
The immune mechanisms that confer protection from influenza infection have not been fully elucidated. Intranasal influenza vaccine imparts immunity against the influenza virus by stimulating production of antibodies that are specific to the disease. Influenza strain-specific serum antibodies to the vaccine have been demonstrated. The intranasal route of administration also stimulates localized mucosal antibody formation and may enhance cytotoxic T-cell formation. In general, patients who receive the vaccine will be immune only to those strains of the virus from which the vaccine was prepared. In one clinical study, protection was afforded against an H3N2 strain that was not well-matched to the H3N2 strain contained in the virus, suggesting that the vaccine provided cross-protection against the variant strain.
Influenza viruses are recognized by the surface antigens they carry, and two such antigens, hemagglutinin (H) and neuraminidase (N) have been identified and are used to classify the various viruses. Subtypes of these strains (H1, H2, H3, N1, N2) are associated with influenza A virus and have been recognized to cause disease in humans. Immunity to these surface antigens increases resistance to infection and decreases the severity of the disease if infection occurs. Eventually, antigenic variation can occur, and immunity to one strain may no longer impart immunity to distantly related subtypes of the virus. Influenza B viruses also exhibit antigenic variation, and new variants of both types of viruses continue to cause widespread epidemics of respiratory disease.
The intranasal influenza vaccine is attenuated and thus, will not produce classic influenza-like illness. However, as the product is a live vaccine, some flu-like symptoms may occur shortly after vaccine receipt.
The intranasal influenza vaccine is administered topically as a fine mist to the inside of the nose. Most of the dose is deposited in the nose and nasopharynx. Post-vaccine antibody titers are generally high enough in healthy young adults and children to provide resistance against infection by influenza virus strains found in the vaccine as well as related strains. The duration of immunity imparted by the intranasal influenza vaccine is unknown; annual revaccination is needed. Influenza may be transmitted by the vaccine recipient to others. The frequency and duration of viral shedding after vaccine receipt have not been established. At least one vaccine strain was recovered from 80% of 98 FluMist recipients during the monitoring period, which was the first 21 days after vaccine receipt. The mean duration of vaccine strain detection was 7.6 +/- 3.4 days.
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