Document 0217
 DOCN  M9460217
 TI    Exposure efficacy and change in contact rates in evaluating prophylactic
       HIV vaccines in the field.
 DT    9408
 AU    Halloran ME; Longini IM Jr; Haber MJ; Struchiner CJ; Brunet RC; Division
       of Biostatistics, Emory University School of Public; Health, Atlanta,
       Georgia 30329.
 SO    Stat Med. 1994 Feb 28;13(4):357-77. Unique Identifier : AIDSLINE
       MED/94233204
 AB    Field studies of the efficacy of prophylactic vaccines in reducing
       susceptibility rely on the assumption of equal exposure to infection in
       the vaccinated and unvaccinated groups. Differential exposure to
       infection could, however, be the goal of other types of intervention
       programme, or it could occur secondary to belief in the protective
       effects of a prophylactic measure, such as vaccination. We call this
       differential exposure the exposure efficacy, or behaviour efficacy. To
       study the relative contribution of unequal exposure to infection and
       differential susceptibility to the estimate of vaccine efficacy, we
       formulate a simple model that explicitly includes both susceptibility
       and exposure to infection. We illustrate this on the example of
       randomized field trials of prophylactic human immunodeficiency virus
       vaccines. Increased exposure to infection in the vaccinated group may
       bias the estimated reduction in susceptibility. The bias in the estimate
       depends on the choice of efficacy parameter, the amount of information
       used in the analysis, the distribution and level of protection in the
       population, and the imbalance in exposure to infection. Sufficient
       increase in contacts in the vaccinated could result in the vaccine being
       interpreted as having an immunosuppressive effect. Estimates of vaccine
       efficacy are generally more robust to imbalances in exposure to
       infection when the detailed history of exposure to infection can be used
       in the analysis or at high levels of protection. The bias also depends
       on the relationship between the distribution of vaccine protection and
       the distribution of behaviour change, which could differ between blinded
       and unblinded trials.
 DE    Adult  AIDS Vaccines/*ADMINISTRATION & DOSAGE  Clinical
       Trials/*STATISTICS & NUMER DATA  Confidence Intervals  Double-Blind
       Method  Female  Human  HIV Infections/*PREVENTION & CONTROL/TRANSMISSION
       Male  Probability  Proportional Hazards Models  Randomized Controlled
       Trials/STATISTICS & NUMER DATA  Risk Factors  Selection Bias  Sex
       Behavior  Support, Non-U.S. Gov't  Support, U.S. Gov't, P.H.S.
       Treatment Outcome  JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).