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Could disease-modifying HIV vaccines cause population-level perversity?
Robert J Smith1, Sally M Blower
1Department of Biomathematics and UCLA AIDS Institute, David Geffen School of Medicine at UCLA, Westwood, CA 90024, USA.
The Lancet. Infectious Diseases
|September 29, 2004
Summary
Disease-modifying HIV vaccines may worsen epidemics if protection is low or transmission fitness is high. However, a significant viral load reduction can prevent this, guiding optimal vaccination strategies.
Area of Science:
- Epidemiology
- Vaccinology
- Mathematical Biology
Background:
- Current HIV vaccines offer limited infection protection but reduce viral load and slow CD4 decline.
- Disease-modifying vaccines may reduce transmission but also risk increasing it, potentially worsening the epidemic.
Purpose of the Study:
- To investigate if disease-modifying HIV vaccines can cause population-level perversity, leading to increased epidemic severity.
- To identify conditions under which such vaccines could be detrimental.
Main Methods:
- Analysis of a mathematical model of HIV transmission.
- Definition and utilization of a 'fitness ratio' to quantify vaccine impact.
- Determination of threshold surfaces for risk behavior change.
Main Results:
- Disease-modifying vaccines with low protection or high fitness ratios increase the probability of epidemic worsening.
- A viral load reduction of 1.5 log(10) or greater prevents perversity, assuming no increase in risk behavior.
- Thresholds for beneficial outcomes depend on fitness ratio, vaccination coverage, and unvaccinated behavior changes.
Conclusions:
- Careful consideration of vaccine characteristics, particularly fitness ratio and viral load reduction, is crucial for preventing perverse outcomes.
- Optimal vaccination strategies must account for potential behavioral changes and population-level effects to ensure epidemic control.