New study confirms worst fears about Merck's HIV vaccine

Five years ago Merck ($MRK) investigators stunned everyone working in the AIDS research field with the news that they were abruptly halting a study of a prospective HIV vaccine after the data began to make clear that it wasn't only failing to guard against the virus, but appeared to increase the risk of becoming infected. Now researchers have followed up to confirm that the worst case scenario was true.

The sudden about-face on the vaccine forced investigators as well as the NIH to do some serious rethinking about the R&D work being done on HIV vaccines. Not knowing exactly what went wrong, another big trial was scrapped on a similar vaccine. And as The New York Times reports today, further work has been carried out in slow motion, delivering at best mixed results.

The new study tracked the health of 1,836 men enrolled in the Merck trial for a further two years. Almost 10% later became infected, with uncircumcised men and men with high levels of antibodies for the Type 5 adenovirus most at risk. As the vaccine was constructed using a weakened adenovirus 5, scientists speculate that may have boosted the presence of CD4 cells in the blood, creating the kind of "target-rich" environment that HIV thrives on.

But that's conjecture. Investigators still aren't certain what went wrong, only concluding that the result had to be biologic. As a cautionary tale, the Merck trial will continue to serve as a reality check for everyone in the field.

- here's the story from The New York Times