Single-Dose Vaccination Among Infants and Toddlers Provides Modest Protection Against Influenza Illness, Which Wanes After 5 Months.

In their first season of vaccination, young children are recommended 2 doses of influenza vaccine, but a 2-dose schedule might be difficult to implement in many countries. Within a cohort study of 742 children aged 6 to <24 months in Managua, Nicaragua, this study estimated effectiveness of partial vaccination from 3 to 9 months postvaccination. Vaccine effectiveness was 74% (95% confidence interval [CI], 24%-91%) within 3 months and 55% (95% CI, 10%-77%) within 4 months. There was not significant protection beyond 5 months. Partial vaccination might confer some benefits but should be followed by a second dose.