Shedding of Ann Arbor strain live attenuated influenza vaccine virus in children 6-59 months of age

Most children 6-59 months of age vaccinated with Ann Arbor strain LAIV shed ≥1 vaccine virus within 11 days of vaccination. Shedding was less common in children 24-59 months of age, a population for whom LAIV is approved for use. Titers of shed vaccine were low, which may explain why secondary transmission of LAIV was observed very infrequently in a previous controlled study conducted with young children in a daycare setting.