The effect size in this hypothetical trial (2.7 fewer infections per 1000 vaccinated) is slightly smaller than the effect size found in the real 2009 HIV vaccine trial (2.8 fewer infections per 1000 vaccinated); so why is the p-value smaller?
The hypothetical trial has less variability. The sample size of the hypothetical trial is larger. . The real trial did not follow a normal distribution. The real trial used an intention to treat analysis