The advanced-phase HIV prevention vaccine trials done in South Africa (HVTN 702) 
and in Thailand (RV144), which both investigated canarypox vectors and 
adjuvanted gp120 proteins, gave rise to different results. The South African 
trial did not find vaccine efficacy, whereas the Thai trial had modest, but 
statistically significant, success with the modified intention-to-treat analysis 
prespecified in the protocols of both studies. An understanding of the 
differences between the studies is required to avoid the possible, but 
erroneous, conclusion that the results from the South African trial negatively 
affect the results of the Thai trial.