Experience from HIV incidence cohorts in Thailand

The documented circulation of 2 distinct subtypes of HIV-1 in Thailand would permit vaccine trials that could measure cross-protection against wild viruses genetically heterologous to vaccine antigen.

Abstract

From early 1990 to early 1992 Nelson et al. found the prevalence of HIV infection among rural northern Thailand village men aged >or= 15 years doubled from 5.3 to 10.4% and among village women of the same age range quadrupled from 0.5 to 2.3%. The incidence rates for HIV in these age groups were 3.2 per 100 person-years (PY) for men and 0.9 for women triple the rate for rural African men recently reported from Uganda an epicenter of the HIV pandemic in Africa. Thailand is likely to be among the first countries to begin trials of candidate vaccines. The protocol for the first Phase 1/Phase II trial was approved in early 1994 by the responsible review committees; by mid 1994 a branched peptide HIV-1 vaccine produced by United Biomedical Inc. is expected to be administered to healthy HIV-negative Thai volunteers by the Thai Red Cross. Other Phase I/Il trials are planned soon by the Vaccine Trials Center of Mahidol University Bangkok using a gp120 vaccine produced by Genentech Inc. The documented circulation of 2 distinct subtypes of HIV-1 in Thailand would permit vaccine trials that could measure cross-protection against wild viruses genetically heterologous to vaccine antigen. However all but one of the cohort studies have been among individuals at heterosexual risk among whom nearly all infections are with HIV-1 env subtype E/Thai genotype A (EA). In contrast IDU in Bangkok have both Ea and subtype B/Thai genotype B (Bb) in a ratio of about 1 : 3. Thus given their high incidence of 11 per 100 PY IDU might make excellent candidates for vaccine efficacy trials designed to study cross protection.