Shedding and immunogenicity of live attenuated influenza vaccine virus in subjects 5-49 years of age


Stan L. Blocka, , , Ram Yogevb, Frederick G. Haydenc, 1, Christopher S. Ambrosed, Wen Zengd and Robert E. Walkerd aKentucky Pediatric and Adult Research, 201 S. 5th Street, Bardstown, KY 40004, United States bChildren’s Memorial Hospital, Chicago, IL, United States cUniversity of Virginia, Charlottesville, VA, United States dMedImmune, Gaithersburg, MD, United States.Received 17 March 2008;  revised 25 June 2008;  accepted 8 July 2008.  Available online 26 July 2008.







Live attenuated influenza vaccine (LAIV) is indicated for influenza prevention in persons 2-49 years of age. This study describes the incidence and duration of vaccine virus shedding and serum immune responses after receipt of LAIV.




A single open-label dose of trivalent LAIV was administered intranasally to 344 subjects in 3 age cohorts: 5-8, 9-17, and 18-49 years of age. Shedding was determined by culture of nasal swabs (on days 1-7, daily; days 9-25, every other day; and day 28). Immunogenicity was measured as serum strain-specific hemagglutinin inhibition (HAI) titers (days 0, 28).






Among subjects aged 5-8 years, 9-17 years, and 18-49 years, 44%, 27%, and 17% of subjects, respectively, shed vaccine virus after vaccination, and the mean number of positive samples per subject was 2.2, 1.8, and 1.5, respectively. Shedding occurred on days 1-11 postvaccination. Shedding incidence peaked on day 2, and maximum observed titers were highest on days 2-3 (<5, <4, and <3 log10 TCID50/mL, respectively, by age group). Despite positive cultures, all titers were <1 log10 TCID50/mL after days 10, 6, and 6, respectively, by age group. Shedding incidence was inversely correlated to age and baseline serum HAI titer. The seroresponse rate (4-fold rise in HAI) to at least 1 strain was 59% (68%, 64%, and 47%, respectively, by age group), and strain-specific rates were higher in baseline seronegative/serosusceptible subjects. Reactogenicity, most commonly runny nose, headache, and sore throat, was not associated with shedding or seroresponse.




This is the first study to comprehensively evaluate nasal shedding of LAIV in individuals 5-49 years of age. Shedding was generally of short duration and at low titers. Study findings support the current recommendation of the Advisory Committee on Immunization Practices that LAIV recipients should only avoid contact with severely immunosuppressed persons (e.g., hematopoietic stem cell transplant recipients) for 7 days after vaccination.