PAS: Live Flu Vaccine Evaluated in Infants

May 6, 2008

In infants who receive flu vaccinations, immunogenicity is higher in those who receive live attenuated influenza vaccine (LAIV) than in those who receive trivalent inactivated influenza vaccine. Also, viral shedding is more common among younger children who receive LAIV than in older children, according to two studies presented this week at the Pediatric Academic Societies and Asian Society for Pediatric Research Joint Meeting in Honolulu.

TUESDAY, May 6 (HealthDay News) -- In infants who receive flu vaccinations, immunogenicity is higher in those who receive live attenuated influenza vaccine (LAIV) than in those who receive trivalent inactivated influenza vaccine. Also, viral shedding is more common among younger children who receive LAIV than in older children, according to two studies presented this week at the Pediatric Academic Societies and Asian Society for Pediatric Research Joint Meeting in Honolulu.

In one study, Bryan M. Harvey, M.D., of Harvey Pediatric Research in Jonesboro, Ark., and colleagues randomly assigned 101 children aged 12 months to 35 months to receive either the LAIV or the trivalent inactivated influenza vaccine. Compared to trivalent inactivated influenza vaccine recipients, the investigators found that LAIV recipients had significantly higher seroconversion rates post-dose one for matched ca H1 (75 percent versus 38 percent) and matched B (64 percent versus 35 percent), and post-dose two for mismatched H1 (73 percent versus 36 percent).

In a second study, Stan L. Block, M.D., of Kentucky Pediatric/Adult Research in Bardstoen, Ky., and a colleague administered a single intranasal dose of LAIV to 200 children in two age groups (6-23 months and 24-60 months). Compared to the older children, the investigators found that the younger children had a higher rate of viral shedding (89 percent versus 69 percent) and a higher mean number of positive shedding samples per subject (2.9 versus 2.7).

"Shedding of vaccine virus after LAIV vaccination is common and occursless frequently in older children," Block's team concludes. "These findings may help to explain why secondary transmission has been observed infrequently in controlled studies in young children."

Both studies were supported by MedImmune.

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