- Multi-center (three distinct counties) and multi-setting (outpatient and ED/Inpatient) case-control study evaluating effectiveness of influenza vaccination against laboratory confirmed influenza during 2003-2004 and 2004-2005 influenza seasons in children 6 to 59 months of age.
- Included: patients presenting to both inpatient (hospitalizations) or outpatient (ED and clinic) visits with acute respiratory illness or febrile illness. Nasal/throat swabs obtained: positive case subject, negative control subject. Then vaccination status obtained.
- Matched for age, time frame, insurance status, presence of underlying medical condition, setting. VE calculated as (1 – aOR) x 100.
- Receipt of all recommended doses of influenza vaccine was associated with halving of laboratory-confirmed influenza-related medical visits among children 6 to 59 months of age in 1 of 2 study years (2004-2005: VE ~60% across age groups was statistically significant).
- This was despite suboptimal matches between vaccine and circulating influenza strains in both years.
- Receipt of partial immunization was not protective against influenza related medical visits.