title: Development of immunity following financial incentives for hepatitis B vaccination among people who inject drugs: A randomized controlled trial.
abstract: BACKGROUND
  People who inject drugs (PWID) are at risk of hepatitis B virus (HBV) but have low rates of vaccination completion. The provision of modest financial incentives increases vaccination schedule completion, but their association with serological protection has yet to be determined.
  
  
  OBJECTIVE
  To investigate factors associated with vaccine-induced immunity among a sample of PWID randomly allocated to receive AUD$30 cash following receipt of doses two and three ('incentive condition') or standard care ('control condition') using an accelerated 3-dose (0,7,21 days) HBV vaccination schedule.
  
  
  METHODS
  A randomised controlled trial among PWID attending two inner-city health services and a field site in Sydney, Australia, assessing vaccine-induced immunity measured by hepatitis B surface antibodies (HBsAb ≥ 10 mIU/ml) at 12 weeks. The cost of the financial incentives and the provision of the vaccine program are also reported.
  
  
  RESULTS
  Just over three-quarters of participants - 107/139 (77%)--completed the vaccination schedule and 79/139 (57%) were HBsAb ≥ 10 mIU/ml at 12 weeks. Vaccine series completion was the only variable significantly associated with vaccine-induced immunity in univariate analysis (62% vs 41%, p<0.035) but was not significant in multivariate analysis. There was no statistically discernible association between group allocation and series completion (62% vs 53%). The mean costs were AUD$150.5, (95% confidence interval [CI]: 142.7-158.3) and AUD$76.9 (95% CI: 72.6-81.3) for the intervention and control groups respectively.
  
  
  CONCLUSIONS
  Despite increasing HBV vaccination completion, provision of financial incentives was not associated with enhanced serological protection. Further research into factors which affect response rates and the optimal vaccination regimen and incentive schemes for this population are needed.
authors.affiliation: Discipline of Addiction Medicine, Central Clinical School (C39), Sydney Medical School, University of Sydney, NSW 2006, Australia. Electronic address: carolyn.day@sydney.edu.au.
authors.forename: Carolyn A
authors.initials: CA
authors.lastname: Day
authors.affiliation: National Drug and Alcohol Research Centre, University of New South Wales, NSW 2052, Australia.
authors.forename: Marian
authors.initials: M
authors.lastname: Shanahan
authors.affiliation: The Kirby Institute, UNSW Australia, Sydney, NSW 2052, Australia.
authors.forename: Handan
authors.initials: H
authors.lastname: Wand
authors.affiliation: Cancer Council NSW, Woolloomooloo, NSW 2010, Australia.
authors.forename: Libby
authors.initials: L
authors.lastname: Topp
authors.affiliation: Discipline of Addiction Medicine, Central Clinical School (C39), Sydney Medical School, University of Sydney, NSW 2006, Australia; Drug Health Services, Royal Prince Alfred Hospital, Missenden Road, Camperdown,NSW 2050, Australia.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Haber
authors.affiliation: Kirketon Road Centre, South Eastern Sydney Local Health District, Kings Cross, NSW 1340 Australia.
authors.forename: Craig
authors.initials: C
authors.lastname: Rodgers
authors.affiliation: Discipline of Addiction Medicine, Central Clinical School (C39), Sydney Medical School, University of Sydney, NSW 2006, Australia.
authors.forename: Rachel
authors.initials: R
authors.lastname: Deacon
authors.affiliation: Department of Epidemiology and Preventive Medicine, Monash University, 89 Commercial Road, Melbourne, Victoria 3004, Australia.
authors.forename: Nick
authors.initials: N
authors.lastname: Walsh
authors.affiliation: The Kirby Institute, UNSW Australia, Sydney, NSW 2052, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Kaldor
authors.affiliation: Kirketon Road Centre, South Eastern Sydney Local Health District, Kings Cross, NSW 1340 Australia.
authors.forename: Ingrid
authors.initials: I
authors.lastname: van Beek
authors.affiliation: The Kirby Institute, UNSW Australia, Sydney, NSW 2052, Australia.
authors.forename: Lisa
authors.initials: L
authors.lastname: Maher
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D055815:Young Adult; D001315:Australia; D006509:Hepatitis B / Q000517:prevention & control; D006510:Hepatitis B Antibodies / Q000097:blood; D017325:Hepatitis B Vaccines / Q000008:administration & dosage / Q000191:economics; D006515:Hepatitis B virus / Q000276:immunology; D009042:Motivation; D011446:Prospective Studies; D015819:Substance Abuse, Intravenous / Q000150:complications; D014611:Vaccination / Q000191:economics / Q000706:statistics & numerical data
chemical_list: D006510:Hepatitis B Antibodies; D017325:Hepatitis B Vaccines
keywords: Contingency management; Financial incentives; Hepatitis B virus; Immunisation; Immunity; People who inject drugs; Randomised controlled trial; Seroconversion