Pitisuttithum P, Nitayaphan S, Chariyalertsak S, et al. - In the RV144 phase 3 vaccine trial in Thailand, 31% efficacy in preventing HIV acquisition was observed in correlation with ALVAC-HIV (vCP1521) and AIDSVAX B/E administration over 6 months. Researchers conducted this trial investigating if and how an additional vaccine boost to the RV144 regimen at varying intervals between the priming vaccine series and the boost affects the immunology in HIV-uninfected individuals aged 20–40 years who were at low risk for HIV infection and in good health. In RV306, a double-blind, placebo-controlled, randomized clinical trial performed at three clinical sites in Thailand.  Participants were randomly assigned to one of five groups and then further randomly assigned to either vaccine or placebo. From Oct 28, 2013, to April 29, 2014, 367 participants were randomly assigned to one of five groups and then were further randomly assigned to either vaccine or placebo. The primary RV144 vaccine series was provided to all participants at months 0, 1, 3, and 6. Group 1 was provided no additional boost, group 2 was provided additional AIDSVAX B/E and ALVAC-HIV (vCP1521) or placebo at month 12, group 3 was provided AIDSVAX B/E alone or placebo at month 12, group 4a was provided AIDSVAX B/E and ALVAC-HIV or placebo at month 15, and group 4b was provided AIDSVAX B/E and ALVAC-HIV or placebo at month 18. As per results, immune responses improve and the efficacy of preventing HIV acquisition might enhance in correlation to receiving additional boosting of the RV144 regimen with longer intervals between the primary vaccination series and late boost. .