title: Influenza vaccine effectiveness in the community and the household.
abstract: BACKGROUND
  There is a recognized need to determine influenza vaccine effectiveness on an annual basis and a long history of studying respiratory illnesses in households.
  
  
  METHODS
  We recruited 328 households with 1441 members, including 839 children, and followed them during the 2010-2011 influenza season. Specimens were collected from subjects with reported acute respiratory illnesses and tested by real-time reverse transcriptase polymerase chain reaction. Receipt of influenza vaccine was defined based on documented evidence of vaccination in medical records or an immunization registry. The effectiveness of 2010-2011 influenza vaccination in preventing laboratory-confirmed influenza was estimated using Cox proportional hazards models adjusted for age and presence of high-risk condition, and stratified by prior season (2009-2010) vaccination status.
  
  
  RESULTS
  Influenza was identified in 78 (24%) households and 125 (9%) individuals; the infection risk was 8.5% in the vaccinated and 8.9% in the unvaccinated (P = .83). Adjusted vaccine effectiveness in preventing community-acquired influenza was 31% (95% confidence interval [CI], -7% to 55%). In vaccinated subjects with no evidence of prior season vaccination, significant protection (62% [95% CI, 17%-82%]) against community-acquired influenza was demonstrated. Substantially lower effectiveness was noted among subjects who were vaccinated in both the current and prior season. There was no evidence that vaccination prevented household transmission once influenza was introduced; adults were at particular risk despite vaccination.
  
  
  CONCLUSIONS
  Vaccine effectiveness estimates were lower than those demonstrated in other observational studies carried out during the same season. The unexpected findings of lower effectiveness with repeated vaccination and no protection given household exposure require further study.
authors: Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI, USA. sohmit@umich.edu
authors: Suzanne E
authors: SE
authors: Ohmit
authors: Joshua G
authors: JG
authors: Petrie
authors: Ryan E
authors: RE
authors: Malosh
authors: Benjamin J
authors: BJ
authors: Cowling
authors: Mark G
authors: MG
authors: Thompson
authors: David K
authors: DK
authors: Shay
authors: Arnold S
authors: AS
authors: Monto
mesh_terms: D000328:Adult; D002648:Child; D015331:Cohort Studies; D017714:Community-Acquired Infections / Q000517:prevention & control / Q000821:virology; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D062486:Public Health Surveillance; D012621:Seasons
chemical_list: D007252:Influenza Vaccines