Two types of influenza vaccine are licensed for use in children: trivalent inactivated influenza
vaccine (TIV) and trivalent live-attenuated influenza vaccine (LAIV). We consider both in our
analysis, though the primary focus is on LAIV, which has been found to be more effective in children
[10]. TIV is administered intramuscularly and is recommended for those aged at least 6 mo.
LAIV is administered intranasally and is recommended only for those between the ages of 2 and
49 y. In both cases, one dose each year is recommended, except for children under 9 y who were
not vaccinated the previous influenza season, for whomtwo doses at least 4 wk apart are recommended
[10]. Antibodies indicating influenza protection emerge about 2 wk after vaccination.