Canarypox in the Coal Mine
A Treatment Issues Editorial
There's been a shakeup in the government's efforts to test a vaccine for HIV. First, the National Institutes of Health (NIH) cancelled plans by its HIV Vaccine Trials Network (HVTN) to launch a large, international study of an HIV vaccine next year. The reason? Disappointing smaller studies with a canarypox-based vaccine combination gave little reason to think it would do any better in an 11,000 person, eighty million dollar trial. This leaves the HVTN all dressed up with no date, its painstakingly built network of global partners standing idle.
Then came news the White House had heeded the advice of Secretary of the Army and recent Enron vice chairman, Thomas E. White, to shift responsibility for another large trial of a similar canarypox vaccine away from the U.S. Army and over to the NIH. This study, planned in cooperation with the Royal Thai Army, is slated to start in that country later this year. So the NIH is back in the canarypox business again -- with little more chance of success than before.
What is the rationale for moving ahead with large, expensive trials before the underlying science to make an effective HIV vaccine has been solved? One answer: infrastructure. Beatrice Hahn, a widely-respected HIV scientist, explained the problem to Nature magazine: "They have made such an investment in training, infrastructure, technology transfer, assays and equipment that at this point it's impossible to pull the plug. This is more than just a vaccine trial." She said.
Indeed, it has the potential to be a disaster. The only thing worse than a minimally active vaccine bombing out in a ballyhooed trial is if it were actually believed to have had a benefit when it didn't. The Thai trial is designed to see if the canarypox combo can cut HIV infection rates in half. Proving that would be terrific -- though highly implausible -- but the problems start if some smaller, ambiguous, degree of protection is reported. In theory, even a modestly protective vaccine could have a significant impact on the pace of the epidemic over many years and large populations. But what would this news do to ongoing or planned trials for more sophisticated vaccine candidates? An ethical quandary over the "best proven treatment" means the landscape for testing vaccines would change altogether.
With a "proven" though marginally effective vaccine having set a standard, it's no longer ethical to conduct trials using placebo. You have to go up against what you already know works. To make an ethical comparison, all study participants would get the standard vaccine, and then only half of them would get the new, hopefully more effective vaccine. A trial's complexity is increased, its size and cost go up, and the time needed to get an answer now stretches out longer and longer. John McNeil, an architect of the surviving canarypox study, estimated that the planned 16,000-person Thai trial could balloon to require 100,000 people if there were a standard vaccine in the picture.
Meanwhile, the HVTN still lacks a mission for its global partners. Although many smaller studies are starting up, the most promising new vaccine candidates are several years from needing large scale testing. What can the vaccine networks do to justify their budgetary existence and keep their infrastructures intact? Must they wait for an AIDS vaccine? Or could they put their assays and equipment to work testing vaccines and preventive measures to combat other global heath disasters just as well?
The U.S./Thai collaboration on HIV vaccine research dates back a decade and is part of a longstanding partnership that has also tackled malaria and dengue virus. An effective vaccine for tuberculosis, malaria or pneumococcal infections would have dramatic health benefits for millions of people -- with and without HIV. Vaccine candidates are languishing in under funded programs at the NIH, the Army and the CDC, as well as at laboratories throughout the world. The emerging capacity and infrastructure to conduct global vaccine trials is too important to let stagnate, but science and good sense demand spending that capital on a candidate with a chance to do some good in the broadest possible view. The time for a large HIV vaccine trial will come, but for now the networks should be thinking outside of the pox.
The Impact of Partially Effective HIV Vaccine on a Population of Intravenous Drug Users in Bangkok, Thailand: A Dynamic Model
This article was provided by Gay Men's Health Crisis. It is a part of the publication GMHC Treatment Issues. Visit GMHC's website to find out more about their activities, publications and services.