A quarter century after a United States health official said there would be a marketable AIDS vaccine within "a minimum of two years", we must face the possibility that it may never happen.

Global investment in HIV vaccine research and development stands at US$759 million, quotes Robert Steinbrook in the New England Journal of Medicine. 

But he notes that a series of unsuccessful trials has reinforced the view that a licensed AIDS vaccine is at least a decade away — and that is "if things go well".

Steinbrook points out that the sole large-scale study of an AIDS vaccine, in Thailand, is currently underway and is expected to continue until 2009.

He says the scientific challenges blocking progress on a vaccine include the genetic diversity and rapid changes of the viral envelope proteins and incomplete understanding of critical immune responses that would prevent infection or control the virus.

Anthony Fauci, the director of the US National Institute for Allergy and Infectious Diseases, is quoted as saying, "We have to leave open the possibility...that we might not ever get a vaccine for HIV.…We are not giving up...but there is a possibility — a clear finite possibility — that that's the case."

Link to full article in the New England Journal of Medicine