Expected epidemiological impacts of introducing an HIV vaccine in Thailand: a model-based analysis

Abstract

Background: The RV144 trial conducted in Thailand was the first to demonstrate modest protective efficacy of an HIV vaccine. Its estimated initial efficacy was ∼74%, but this waned considerably over time.

Methods: We developed a mathematical model to reflect historical and current HIV trends across different at-risk populations in Thailand. The model was used to estimate the expected number of infections that would be averted if a vaccine with outcome characteristics similar to the RV144 vaccine was implemented in Thailand at varying levels of coverage.

Results: In the absence of a vaccine, we projected roughly 65,000 new HIV infections among adults during the period between 2011 and 2021. Due to the waning efficacy of the vaccine, vaccination campaigns were found to have modest long-term public health benefit unless re-vaccination occurred. We forecast that an RV144-like vaccine with coverage of 30% of the population would lead to a 3% reduction in HIV incidence during the next 10 years. In comparison, 30% coverage of annual or biennial re-vaccination with the vaccine was found to result in 23% and 14% reductions in incidence, respectively. Coverage of 60% without re-vaccination resulted in a 7% reduction. Epidemiological outcomes were found to depend primarily on three factors: vaccination coverage, vaccine efficacy, and the duration of protection the vaccine provided.

Discussion: Due to the short duration of protection the vaccine provides without re-vaccination, our model predicts modest benefit from a vaccination campaign with an RV144-like HIV vaccine in Thailand. Annual or biannual re-vaccination is predicted to greatly increase the long-term public health benefits of a vaccination campaign. The feasibility of vaccine implementation, as well as its economic viability, remains to be determined.