The Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC) has released a supplement to the 2003 recommendations regarding prevention and control of influenza. The report summarizes guidelines for using intranasally administered, trivalent, cold-adapted, live, attenuated influenza vaccine (LAIV), which was approved for use in the United States on June 17, 2003.

Also included in the document is information about vaccine composition and mechanisms of action; comparison between LAIV and trivalent inactivated influenza vaccine; effectiveness and safety of LAIV; transmission and stability of LAIV viruses; recommendations and contraindications for using LAIV; and dosage and administration of LAIV. The supplement appears in the September 26, 2003 recommendations and reports series of Morbidity and Mortality Weekly Report.

Influenza prevention relies primarily on vaccination. Until recently, only inactivated influenza vaccine administered by injection was available for use in the United States. This year, the intranasal, trivalent, coldadapted, LAIV was approved for use in healthy persons five to 49 years of age. LAIV adds an option for vaccinating healthy persons in this age range who want to avoid influenza or who have close contact with persons at high risk for experiencing serious complications from influenza infection. Identical to inactivated vaccine, LAIV contains strains representative of each of the three influenza viruses recommended by the U.S. Public Health Service.

According to ACIP, the major differences between LAIV and inactivated influenza vaccine are:

• LAIV contains attenuated viruses still capable of replication, whereas inactivated influenza vaccine contains killed viruses.

• LAIV is administered intranasally by sprayer, whereas inactivated influenza vaccine is administered intramuscularly by injection.

• LAIV is more expensive.

• LAIV is approved for use only in healthy persons from five to 49 years of age; inactivated vaccine is approved for use in persons six months or older, including those who are healthy and those with chronic medical conditions.

Recommendations for Using LAIV

LAIV is an option for healthy persons in close contact with groups at high risk and those wanting to avoid influenza. Possible advantages of LAIV include its potential to induce a broad mucosal and systemic immune response, its ease of administration, and the acceptability of an intranasal rather than intramuscular route of administration. In randomized, double-blind, placebocontrolled trials, LAIV was 92 percent efficacious in preventing influenza in children. In adults, the difference between the efficacy rate for LAIV (85 percent) and inactivated influenza vaccine (71 percent) was statistically insignificant.

PERSONS WHO SHOULD NOT BE VACCINATED WITH LAIV

According to ACIP, the following groups should not be vaccinated with LAIV:

• Persons younger than five years or 50 years or older

• Persons with asthma, reactive airways disease, or other chronic disorders of pulmonary or cardiovascular systems; persons with other underlying medical conditions, including such metabolic diseases as diabetes, renal dysfunction, and hemoglobinopathies; or persons with known or suspected immunodeficiency disease or who are receiving immunosuppressive therapies

• Children or adolescents receiving aspirin or other salicylates because of the association of Reye's syndrome with wild-type influenza infection

• Persons with a history of Guillain-Barré syndrome

• Pregnant women

• Persons with a history of hypersensitivity, including anaphylaxis, to any of the components of LAIV or to eggs.

TIMING OF VACCINATION

The best time to vaccinate is usually in October and November, but physicians can begin vaccinating with LAIV as supplies are available. Children five to eight years of age who have never received influenza vaccine should receive LAIV for the first time in October or earlier because they need a second dose six to 10 weeks after the initial dose.

DOSAGE AND ADMINISTRATION

Approximately 0.25 mL is sprayed into the first nostril while the recipient is in the upright position. An attached dose-divider clip is removed from the sprayer to administer the second half of the dose into the other nostril. If the vaccinee sneezes after administration, the dose should not be repeated.

ACIP recommends that LAIV be administered annually according to the following schedule:

• Children five to eight years of age previously unvaccinated at any time with LAIV or inactivated influenza vaccine should receive two doses of LAIV separated by six to 10 weeks.

• Children five to eight years of age previously vaccinated at any time with LAIV or inactivated influenza vaccine should receive one dose of LAIV. They do not require a second dose.

• Persons nine to 49 years of age should receive one dose of LAIV.

LAIV can be administered to persons with minor acute illnesses (e.g., diarrhea or mild upper respiratory tract infection with or without fever). If clinical judgment indicates nasal congestion is present that might impede delivery of the vaccine to the nasopharyngeal mucosa, deferral of administration should be considered until resolution of the illness.

It is unknown whether concurrent administration of LAIV with other vaccines affects the safety or efficacy of LAIV or the simultaneously administered vaccine. The ACIP recommends that two live vaccines not administered on the same day should be administered four or more weeks apart when possible. An inactivated vaccine can be administered simultaneously or at any time before or after LAIV.

USE OF INFLUENZA ANTIVIRAL MEDICATIONS

Because influenza antivirals reduce replication of influenza viruses, LAIV should not be administered until 48 hours after cessation of antiviral therapy, and influenza antiviral medications should not be administered for two weeks after receipt of LAIV.

Side Effects and Adverse Reactions

The incidence of adverse events possibly complicating influenza (e.g., pneumonia, bronchitis, bronchiolitis, or central nervous system events) was not statistically different in LAIV and placebo recipients five to 49 years of age.

Signs and symptoms reported more often in vaccinees than placebo recipients included runny nose or nasal congestion, headache, fever, vomiting, abdominal pain, and myalgias. These symptoms were associated more often with the first dose and were self-limited. In adults, runny nose or nasal congestion, headache, and sore throat have been reported more often in vaccinees than placebo recipients.

Until more data are acquired, persons at high risk for experiencing complications from influenza infection (e.g., immunocompromised patients; patients with asthma, cystic fibrosis, or chronic obstructive pulmonary disease; or persons 65 years or older) should not be vaccinated with LAIV.