Expectation of volunteers towards the vaccine efficacy of the prime-boost HIV vaccine phase III trial during unblinding

Abstract

A Phase III community-based HIV vaccine trial using the ALVAC-HIV and AIDSVAX B/E prime-boost regimen (RV144) showed a modest vaccine efficacy of 31.2% against HIV acquisition. Participant's understanding of the trial is a key element of its success. This study aimed to understand participant's expectation and response to the overall results of the trial as well after unblinding. Using an open-ended questionnaire, data were collected from 400 participants who came for the unblinding visit. Fifty-three percent received the vaccine and 47% were placebo recipients. The median age was 30 years (range: 22-37). The observed vaccine efficacy of 31.2% was lower than expected by 67.75% of participants compared to higher than expected (by 6%), as expected (by 11.25%), and those with no expectation (15%). A majority of participants (71.5%) were happy and proud, and indicated that it was a good result. The rest were sad or disappointed (22.75%) or acquiescent (5.75%). After unblinding, 67.92% of the vaccine recipients had a positive response and 32.08% were acquiescent. Among placebo recipients, 85.11% were acquiescent and 10.11% indicated that being assigned to the vaccine group would have been better even though vaccine efficacy was only 31.2%. Despite the modest vaccine efficacy, a majority of study participants acknowledged the value of the trial and hoped that information from RV144 could be used for future vaccine development.

FIG. 1.

Expectation of participants for RV144 vaccine efficacy before their unbinding.