In a rare piece of good news, the Joint United Nations Programme on HIV/AIDS (UNAIDS) last month cut its estimate of the number of people infected with HIV worldwide. The revised figures brought the estimate of those infected down from 39.5 million to 33.2 million, and put the number of new infections for 2007 at 2.5 million, down from what the agency now says was a late-1990s peak of more than 3 million per year. The revised statistics are particularly encouraging for India, where the agency says that 2.5 million people are infected with HIV, a figure that is less than half its previous estimate.

But most of this change is accounted for by more accurate sampling techniques, and the new numbers sadly reflect little significant progress in combating AIDS on the ground. That is especially true in sub-Saharan Africa where UNAIDS reports that 68% of all HIV infections and 76% of AIDS deaths now occur. In these countries, women are often unable to insist on condom use, concurrent relationships contribute to the spread of the disease, and fewer than one-third of patients that could benefit have access to the antiretroviral drugs that can considerably extend life expectancy.

Although immunologists and virologists are making progress in understanding, for example, how HIV affects the mucosal surfaces of the body — a process that seems to contribute greatly to HIV's destructive toll on the immune system — the search for a preventative vaccine has stalled. Only this autumn, a trial for a candidate vaccine from Merck was halted because it proved to be ineffective, and actually made some subjects more vulnerable to infection (see Nature 450, 325; 2007). Some researchers are now claiming that disappointing lab results for this vaccine earlier in its development should have prevented it from getting to full-blown clinical trials. Those in the field have recently made attempts to ensure that new vaccine candidates meet rigorous scientific standards agreed to by the entire field — but this initiative began after the Merck vaccine had entered large clinical trials.

It seems that in vaccine development, researchers waited too long to coordinate their efforts fully. That could provide a lesson for the parallel quest for an effective microbicide — a chemical prevention method whose use, importantly, would be controlled by women. All the results of large microbicide trials to date have been disappointing — and duplicative microbicide trials are still being planned (see Nature 448, 110–111; 2007). It is not clear that the most promising microbicide candidates are those that are being advanced most rapidly into trials, nor is there any consensus about what the most scientifically promising candidate would look like.

These are issues the microbicide field needs to resolve. With no vaccine in sight, the microbicide researchers are arguably those best placed to deliver something that will fundamentally alter the shape of the AIDS pandemic. That way, UNAIDS might one day deliver a downward estimate in the worldwide HIV burden that can be attributed to genuine progress against the disease, rather than to better statistical sampling.