Did the H1N1 Vaccine Reduce the Risk of Admission with XXXX during the Pandemic?

@entity1 @entity1479 @entity55 @entity683 @entity281
BACKGROUND: The extent to which A(H1N1)pdm09 @entity683 vaccines prevented hospital admissions with @entity55 and @entity683 (P_I) during the 2009 pandemic remains poorly understood. We evaluated the effectiveness of the A(H1N1)pdm09 and seasonal @entity683 vaccines (TIV) used during the 2009 mass vaccination campaign in Manitoba (Canada) in preventing P_I hospitalization. METHODS: A population-based record-linkage nested case-control study. Cases (N = 1,812) were @entity1 hospitalized with @entity683 ( @entity1479 -10:J09-J11) or @entity55 ( @entity1479 -10:J12-J18) during the study period. Age-, gender- and area of residence-matched controls (N = 7,915) were randomly sampled from Manitoba's Population Registry. Information on receipt of A(H1N1)pdm09 vaccine and TIV was obtained from the Manitoba Immunization Monitoring System, a province-wide vaccine registry. RESULTS: Overall, the adjuvanted A(H1N1)pdm09 vaccine was 27% (95%CI 13-39%) effective against P_I hospitalization >=  14 days following administration. Effectiveness seemed lower among older (>=  65 years) adults (10%; -16-30%), particularly when compared to under-5 @entity1 (58%; 30-75%). The number-needed-to-vaccinate to prevent 1 P_I admission was lowest among <4 year-olds (928) and >= 65 years (1,721). VE against hospitalization with laboratory-confirmed A(H1N1)pdm09 was 70% (39-85%) overall and (91%; 62-98%) >=  14 days following vaccination. DISCUSSION: Our data suggest that the adjuvanted A(H1N1)pdm09 vaccine was effective in preventing about 55-60% of P_I hospitalizations among @entity1 and younger adults who were at much higher risk of @entity281 . Unfortunately, the vaccine was less effective among 65 or older adults. Despite that the vaccine still had a significant population-based impact especially among the very young (<5) and the older (>=  65 years).
