The world's largest Phase III HIV vaccine trial, currently under way in Thailand, will be extended by a year because of difficulty in recruiting volunteers for the study, The Nation reports. The trial is testing the use of two HIV vaccines--VaxGen's AIDSVAX and Aventis Pasteur's ALVAC--as a combination approach to boost immune system defenses against HIV and prevent HIV infection. The trial needs 16,000 HIV-negative volunteers, but only 5,224 to date have passed the rigorous screening process for the study. Supachai Rerks-ngarm, the trial's chief investigator, says recruitment for the study will be extended another year. Health officials say an ineffective public relations campaign to recruit volunteers for the study resulted in the lower-than-expected enrollment in the clinical trial.