AIDS Res Hum Retroviruses. 2014 Nov;30(11):1041-5.

Expectation of Volunteers Towards the Vaccine Efficacy of the Prime-Boost HIV Vaccine Phase III Trial During Unblinding


Kessuda Khowsroy1, Jittima Dhitavat1*, Yupa Sabmee1, Pataramon Laowarakul1, Jutarat Wattanakitwichai1, Jiraporn Auetian1, Kannika Lothong1, Roongtip Boondao1, Sarawan Maythaarttaphong1, Sunee Yaemwong1, Jean-Louis Excler2, Supachai Rerks-Ngarm3, Punnee Pitisuttithum1

1 Vaccine Trial Centre, Faculty of Tropical Medicine, Mahidol University, 420/6 Rajvithi Road, Ratchathewi, Bangkok 10400, Thailand

2 U.S. Military HIV Research Program, Bethesda, Maryland 20817, U.S.A.

3 Department of Disease Control, Ministry of Public Health, Nonthaburi 11000, Thailand



A Phase III community-based HIV vaccine trial using the ALVAC-HIV and AIDSVAXÒ 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% expressed 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.

PMID: 24906244



A community-based efficacy Phase III trial (RV144) of the prime-boost regimen, using ALVAC-HIV (vCP1521) (Sanofi Pasteur) and AIDSVAXÒ B/E (Global Solutions for Infectious Diseases) to evaluate the vaccine efficacy, was conducted from October 2003 to June 2009 in Thailand.1 A total of 16,402 healthy HIV-uninfected Thai participants, aged between 18 and 30 year-old, were enrolled. RV144 provided the first evidence that HIV vaccine protection against HIV acquisition could be achieved with an estimated vaccine efficacy of 31.2% at 42 months post enrollment.2

An initial in-depth discussion with structured interview to determine expectation of participants prior to the announcement of the vaccine efficacy result on September 24, 2009 was conducted in 64 RV144 volunteers from December 2008 to January 2009. Most participants (47/64, 73.4%) expected the vaccine to be efficacious and almost 40% (25/63) to be 100% efficacious.3   With such high expectations from participants, it is important for researcher to understand their feelings during unblinding. The objectives of the present study were to describe and understand the participants’ expectation and their feelings with regard to the vaccine efficacy result during unblinding.


Expectation of participants for vaccine efficacy before their unblinding are shown in Fig 1 and response of the participants on vaccine efficacy of 31.2% in Table 1. Despite the RV144 modest efficacy against HIV acquisition, which did not meet participant’s expectation, the majority of participants expressed their satisfaction and acknowledgement to the conduct and value of the trial.


Table 1. Opinion of study participants about the clinical trial and as study participants.

JD tab1

a Number of participants who provided feedback out of the 400 participants.


Important of the study:

Knowledge of expectation of trial participants may help researchers address each participant’s need for appropriate explanation of the objectives of future HIV vaccine efficacy trials.



  1. Rerks-Ngarm S, Pitisuttithum P, Nitayaphan S, et al. Vaccination with ALVAC and AIDSVAX to prevent HIV-1 infection in Thailand. New Engl J Med 2009; 361: 2209-2220.
  2. World Health Organisation. Recommendations arising from the expert consultation on the future utility of the RV 144 vaccine regimen. March 16-18, 2010 Bangkok, Thailand. Available at Accessed July 28, 2015.
  3. Pitisuttithum P, Indrasuta C, Khowsroy K, et al. Expectation of participants towards vaccine’s efficacy in the phase III vaccine trial in Thailand. In The 9th International Congress on AIDS and the Pacific (ICAAP), Bali, Indonesia, 2009 [Abstract WEPB 026]. Available at Accessed July 28, 2015.


Acknowledgements: The authors are grateful to all study participants and staff at study sites. This work was supported by a cooperative agreement (W81XWH-11-2-0174) between the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc. and the U.S. Department of Defense. This research was funded in part by the U.S. National Institute of Allergy and Infectious Diseases, U.S. National Institutes of Health.



Jittima Dhitavat, MD, DPhil

Assistant Professor

Vaccine Trial Center, Faculty of Tropical Medicine, Mahidol University

420/6 Rajvithi Road, Ratchathewi, Bangkok 10400, Thailand






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