title: Optimal timing of influenza vaccination in patients with human immunodeficiency virus: a Markov cohort model based on serial study participant hemoagglutination inhibition titers.
abstract: BACKGROUND
  Seasonal influenza vaccination offers one of the best population-level protections against influenza-like illness (ILI). For most people, a single dose prior to the flu season offers adequate immunogenicity. HIV+ patients, however, tend to exhibit a shorter period of clinical protection, and therefore may not retain immunogenicity for the entire season. Building on the work of Nosyk et al. (2011) that determined a single dose is the optimal dosing strategy for HIV+ patients, we investigate the optimal time to administer this vaccination.
  
  
  METHODS
  Using data from the "single dose" treatment arm of an RCT conducted at 12 CIHR Canadian HIV Trials Network sites we estimated semimonthly clinical seroprotection levels for a cohort (N=93) based on HAI titer levels. These estimates were combined with CDC attack rate data for the three main strains of seasonal influenza to estimate instances of ILI over different vaccination timing strategies. Using bootstrap resampling of the cohort, nine years of CDC data, and parameter distributions, we developed a Markov cohort model that included probabilistic sensitivity analysis. Cost, quality adjusted life-years (QALYs), and net monetary benefits are presented for each timing strategy.
  
  
  RESULTS
  The beginning of December is the optimal time for HIV+ patients to receive the seasonal influenza vaccine. Assuming a willingness-to-pay threshold of $50,000, the net monetary benefit associated with a Dec 1 vaccination date is $19,501.49 and the annual QALY was 0.833744.
  
  
  CONCLUSIONS
  Our results support a policy of administering the seasonal influenza vaccination for this population in the middle of November or beginning of December, assuming nothing is know about the upcoming flu season. But because the difference in between this strategy and the CDC guideline is small-12 deaths averted per year and a savings of $60 million across the HIV+ population in the US-more research is needed concerning strategies for subpopulations.
authors.affiliation: Centre for Health Evaluation and Outcome Sciences, 588 - 1081 Burrard Street, St. Paul's Hospital, Vancouver, BC, V6Z 1Y6 Canada; School of Population and Public Health, University of British Columbia, 2206 East Mall, Vancouver, BC, V6T 1Z3 Canada. Electronic address: gwerker@cheos.ubc.ca.
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Werker
authors.affiliation: School of Population and Public Health, University of British Columbia, 2206 East Mall, Vancouver, BC, V6T 1Z3 Canada.
authors.forename: Behnam
authors.initials: B
authors.lastname: Sharif
authors.affiliation: Centre for Health Evaluation and Outcome Sciences, 588 - 1081 Burrard Street, St. Paul's Hospital, Vancouver, BC, V6Z 1Y6 Canada; CIHR Canadian HIV Trials Network, 588 - 1081 Burrard Street, St. Paul's Hospital, Vancouver, BC, V6Z 1Y6 Canada.
authors.forename: Huiying
authors.initials: H
authors.lastname: Sun
authors.affiliation: CIHR Canadian HIV Trials Network, 588 - 1081 Burrard Street, St. Paul's Hospital, Vancouver, BC, V6Z 1Y6 Canada; Division of Infectious Diseases, University of Ottawa, 451 Smyth Road, Ottawa, ON, K1H 8M5 Canada.
authors.forename: Curtis
authors.initials: C
authors.lastname: Cooper
authors.affiliation: Centre for Health Evaluation and Outcome Sciences, 588 - 1081 Burrard Street, St. Paul's Hospital, Vancouver, BC, V6Z 1Y6 Canada; School of Population and Public Health, University of British Columbia, 2206 East Mall, Vancouver, BC, V6T 1Z3 Canada.
authors.forename: Nick
authors.initials: N
authors.lastname: Bansback
authors.affiliation: Centre for Health Evaluation and Outcome Sciences, 588 - 1081 Burrard Street, St. Paul's Hospital, Vancouver, BC, V6Z 1Y6 Canada; School of Population and Public Health, University of British Columbia, 2206 East Mall, Vancouver, BC, V6T 1Z3 Canada; CIHR Canadian HIV Trials Network, 588 - 1081 Burrard Street, St. Paul's Hospital, Vancouver, BC, V6Z 1Y6 Canada. Electronic address: aslam.anis@ubc.ca.
authors.forename: Aslam H
authors.initials: AH
authors.lastname: Anis
mesh_terms: D006679:HIV Seropositivity; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007115:Immunization Schedule; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000191:economics; D007251:Influenza, Human / Q000191:economics / Q000517:prevention & control*; D008390:Markov Chains; D008962:Models, Theoretical; D009010:Monte Carlo Method; D016032:Randomized Controlled Trials as Topic; D014611:Vaccination / Q000191:economics*
chemical_list: D007252:Influenza Vaccines
keywords: CIHR; Canadian Institutes of Health Research; HAI; HIV; ILI; Markov cohort model; NMB; Optimal strategy; Probabilistic sensitivity analysis; QALY; QoL; Seasonal influenza; Timing; WtP; hemoagglutination inhibition; influenza-like-illness; net monetary benefit; quality adjusted life-years; quality of life; willingness-to-pay