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1994-06-25
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Document 0598
DOCN M9460598
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).