February 27, 2003
Dr. Steven G. Self, a professor of biostatistics at the University of Washington, said that the company should have lowered the level of confidence with which it said that the vaccine appeared to protect blacks, Asians and other non-Hispanic minorities from infection by HIV.
VaxGen President Dr. Donald P. Francis said there was some debate among statisticians about the proper adjustments but called it a "a tangential issue." Even with the adjustments, he said, the results showing efficacy in minorities would still be statistically significant.
VaxGen reported Monday that its vaccine was ineffective over all in a trial of 5,400 participants. But it said that in a subset of 500 non-Hispanic minorities, the vaccine reduced infection by 66.8 percent, a statistically significant result. The company has since been criticized by scientists and AIDS activists for stressing conclusions based on a small number of patients.
VaxGen reported that its finding for the minority subgroup had a confidence interval of 30.2 percent to 84.2 percent. That meant that there was a 95 percent probability that the actual efficacy of the vaccine in the subgroup was between those points. But Self said that by his calculation the low end of the confidence interval should be just above zero. That is because the company should have lowered its confidence to account for the fact that it analyzed multiple subgroups of patients. If the data are cut enough ways, some effectiveness can almost always be found, he said, so such "penalties" to the interval are taken to guard against false positive conclusions. "It's probably an honest error," Self said. But he said the fact that the lower bound was still above zero still provided "some marginal statistical evidence that there is some efficacy in that subgroup."