Influenza vaccine effectiveness among adult patients in a University of Lyon hospital (2004-2009).

The aim of this study was to estimate influenza vaccine effectiveness (IVE) against laboratory-confirmed influenza among hospitalized patients. A case-control investigation was based on the prospective surveillance of influenza-like illness (ILI) during five flu seasons. We compared influenza-positive cases and influenza-negative controls. Unadjusted overall IVE was 62% (95% confidence interval 24% to 81%). We found that IVE was lower during the 2004-05 flu season (11%; 95% CI -232% to 76%) when the vaccine and circulating viruses were mismatched. Expansion of the study to other hospitals could provide IVE estimates earlier in the season, for different age groups and emerging virus strains.

Risk of influenza-like illness in an acute health care setting during community influenza epidemics in 2004-2005, 2005-2006, and 2006-2007: a prospective study.

BACKGROUND: The person-to-person transmission of influenza-like illness (ILI) and influenza has been described mostly in long-term care units. Studies in acute hospital settings are rare and mostly retrospective. METHODS: We prospectively estimated the relative risk (RR) of hospital-acquired (HA) ILI during hospitalization according to in-hospital exposures to contagious individuals. Surveillance of ILI and laboratory-confirmed influenza was undertaken at Edouard Herriot Hospital (1100 beds) during 3 influenza seasons. A total of 21 519 patients and 2153 health care workers (HCWs) from 2004 to 2007 were included. The RR of HA-ILI in patients was calculated according to exposure to other contagious patients and HCWs. RESULTS: For patients exposed to at least 1 contagious HCW compared with those with no documented exposure in the hospital, the RR of HA-ILI was 5.48 (95% confidence interval [CI], 2.09-14.37); for patients exposed to at least 1 contagious patient, the RR was 17.96 (95% CI, 10.07-32.03); and for patients exposed to at least 1 contagious patient and 1 contagious HCW, the RR was 34.75 (95% CI, 17.70-68.25). CONCLUSIONS: Hospitalized patients exposed to potentially infectious patients and HCWs with ILI inside the hospital are at greater risk for HA-ILI. Such results identify priorities regarding preventive measures for seasonal or pandemic influenza.