Vaccines

The day the discovery of the human immunodeficiency virus (HIV) was announced in 1984, the then US Health Secretary Margaret Heckler forecast that a vaccine against the newly discovered virus should not be too difficult to develop. She said: “We hope to have such a vaccine ready for testing in approximately two years…yet another terrible disease is about to yield to patience, persistence and outright genius".¹

More than a quarter-century later, HIV vaccine researchers are still looking for a vaccine that would offer a significant degree of protection against HIV infection. HIV has turned out to have several unique properties that make the development of a vaccine harder than developing one against other viral infections.

There have only ever been four large phase III efficacy trials of HIV vaccines in humans. The first two were of different versions of a vaccine called AIDSVAX; we learnt in 2003 that neither version prevented infection. The third was the STEP trial, which closed in September 2007 - this vaccine, which had looked promising in animal studies, proved not only to have no effect in humans but actually to increase the likelihood of infection in a subset of participants.

In October 2009 however, the vaccine studied in the fourth such efficacy trial, the RV144 trial, proved to be modestly, and unexpectedly, efficacious, reducing HIV infections in recipients by 31%.

This, and a number of promising animal study results, have revitalised interest in HIV vaccine research, and most scientists now believe that an effective HIV vaccine is possible, even if few are prepared to predict when one might be available. Currently, however, no large phase III efficacy trials are being conducted though there is one phase IIb trial, HVTN 505, taking place in in 2200 volunteers in the US. Phase IIb trials are ‘test of concept’ trials, which can begin to examine a candidate vaccine’s efficacy.

The field is in a period of retrenchment, conducting, in the main, smaller trials of novel vaccines and examining ways to improve the immunological efficacy of formulations already used.