Estimating the demand for a preventive HIV vaccine: why we need to do better. Reliable estimates would help in achieving several policy and advocacy objectives

The marginal willingness-to-pay for attributes of a hypothetical HIV vaccine

This paper estimates the marginal willingness-to-pay for attributes of a hypothetical HIV vaccine using discrete choice modeling. We use primary data from 326 respondents from Bangkok and Chiang Mai, Thailand, in 2008-2009, selected using purposive, venue-based sampling across two strata. Participants completed a structured questionnaire and full rank discrete choice modeling task administered using computer-assisted personal interviewing. The choice experiment was used to rank eight hypothetical HIV vaccine scenarios, with each scenario comprising seven attributes (including cost) each of which had two levels. The data were analyzed in two alternative specifications: (1) best-worst; and (2) full-rank, using logit likelihood functions estimated with custom routines in Gauss matrix programming language. In the full-rank specification, all vaccine attributes are significant predictors of probability of vaccine choice. The biomedical attributes of the hypothetical HIV vaccine (efficacy, absence of VISP, absence of side effects, and duration of effect) are the most important attributes for HIV vaccine choice. On average respondents are more than twice as likely to accept a vaccine with 99% efficacy, than a vaccine with 50% efficacy. This translates to a willingness to pay US$383 more for a high efficacy vaccine compared with the low efficacy vaccine. Knowledge of the relative importance of determinants of HIV vaccine acceptability is important to ensure the success of future vaccination programs. Future acceptability studies of hypothetical HIV vaccines should use more finely grained biomedical attributes, and could also improve the external validity of results by including more levels of the cost attribute.

A novel retinoic acid, catechin hydrate and mustard oil-based emulsion for enhanced cytokine and antibody responses against multiple strains of HIV-1 following mucosal and systemic vaccinations

Non-replicating protein- or DNA-based antigens generally require immune-enhancing adjuvants and delivery systems. It has been particularly difficult to raise antibodies against gp120 of HIV-1, which constitutes an important approach in HIV vaccine design. While almost all effort in adjuvant research has focused on mimicking the pathogens and the danger signals they engender in the host, relatively little effort has been spent on nutritive approaches. In this study, a new nutritive immune-enhancing delivery system (NIDS) composed of vitamin A, a polyphenol-flavonoid, catechin hydrate, and mustard oil was tested for its adjuvant effect in immune responses against the gp120 protein of HIV-1(CN54). Following a combination of two mucosal and two systemic vaccinations of mice, we found significant enhancement of both local and systemic antibodies as well as cytokine responses. These data have important implications for vaccine and adjuvant design against HIV-1 and other pathogens.

Preventive HIV vaccine acceptability and behavioral risk compensation among high-risk men who have sex with men and transgenders in Thailand

Thailand, with the highest number of volunteers to have participated in preventive HIV-1 vaccine trials globally, may be an early adopter of HIV vaccines. We conducted a mixed methods investigation, including 30 in-depth interviews and a venue-based survey. We used a structured questionnaire including conjoint analysis and a fractional factorial experimental design to assess preventive HIV vaccine acceptability and risk compensation among 255 high-risk men who have sex with men (MSM) and transgenders (mean age=26.6 years). HIV vaccine acceptability ranged from 31.6 to 73.8 on a 100-point scale; mean=58.3 (SD=17.1). Vaccine-induced seropositivity (VISP) had the greatest impact on acceptability, followed by efficacy, side effects, duration of protection, out-of-pocket cost and social saturation. Over one-third (34.6%) reported intentions to increase post-vaccination risk behaviors in response to a highly efficacious HIV vaccine. Social and structural interventions to promote HIV vaccine uptake as a prosocial behavior, provide accessible assays to detect VISP, and subsidize vaccine costs, and support for uptake of partially efficacious vaccines in the context of combination prevention, will facilitate HIV vaccine dissemination in Thailand.

Preventive HIV vaccine acceptability and behavioral risk compensation among a random sample of high-risk adults in Los Angeles (LA VOICES)

OBJECTIVE

To assess HIV vaccine acceptability among high-risk adults in Los Angeles.

STUDY SETTING

Sexually transmitted disease clinics, needle/syringe exchange programs, Latino community health/HIV prevention programs.

STUDY DESIGN

Cross-sectional survey using conjoint analysis. Participants were randomly selected using three-stage probability sampling.

DATA COLLECTION

Sixty-minute structured interviews. Participants rated acceptability of eight hypothetical vaccines, each with seven dichotomous attributes, and reported post-vaccination risk behavior intentions.

PRINCIPAL FINDINGS

Participants (n=1164; 55.7 percent male, 82.4 percent ethnic minority, mean age=37.4 years) rated HIV vaccine acceptability from 28.4 to 88.6; mean=54.5 (SD=18.8; 100-point scale). Efficacy had the greatest impact on acceptability, followed by side effects and out-of-pocket cost. Ten percent would decrease condom use after vaccination.

CONCLUSIONS

Findings support development of social marketing interventions to increase acceptability of "partial efficacy" vaccines, behavioral interventions to mitigate risk compensation, and targeted cost subsidies.