Delay, Doubt and Dollars: Exploring Delay and Probability Discounting of Free and Paid HIV Vaccines among Sexual and Gender Minorities

This study investigated how delays and uncertainties shape the perceived value of hypothetical HIV vaccines under different cost conditions among sexual and gender minorities (SGMs). In Experiment 1 (N = 260), participants chose between a 60% effective vaccine available immediately and a 99% effective vaccine with varying delays. Experiment 2 (N = 246) assessed choices between a 55% effective vaccine with certain availability and a 95% effective vaccine with uncertain availability. Participants were randomly assigned to free or $150 fee conditions. Hyperbolic discounting models effectively described delay (R² = 0.96-0.99) and probability discounting (R² = 0.95-0.99). Vaccine cost did not significantly affect discounting, while age and STI testing history did, with effects varying by delay versus probability context. Gay or bisexual identity, health insurance status, and political orientation additionally predicted probability discounting. The findings demonstrate the utility of behavioral economic models for quantifying HIV vaccine valuation prior to market availability.