Posted on behalf of Priya Shetty

AIDS vaccine research was given a boost last year by the discovery of super-antibodies that can vanquish most strains of HIV. But just as the field celebrated this breakthrough, the finding that antiretroviral drugs can be startlingly effective prophylactics against HIV infection began to stir discussion about whether a vaccine was really that important after all.

The buzz over treatment as prevention came to a head at the International AIDS Society meeting in Rome this week.

Pre-exposure prophylaxis (PrEP) – giving antiretrovirals like tenofovir to HIV-negative people – looks to be highly effective at reducing the risk of infection. The TDF2 study in Botswana cut the risk of infection in heterosexual people by up to 78%, and the Partners PrEP trial reduced the chance of infection by up to 73%. This Partners PreP data was so compelling that the trial was stopped a year and a half early. The long-awaited HPTN 052 trial presented this week also showed for the first time that by starting antiretroviral treatment early, HIV-positive people reduce the risk of transmitting the virus by 96%.

The standing ovation from the crowded auditorium when all three studies were presented late yesterday was understandable – for too long, HIV prevention has relied on behavioural approaches such as condom use, which are notoriously hard to implement.

But this excitement should be tinged with caution, say vaccine researchers. Gary Nabel, head of the US National Institutes of Health’s Vaccine Research Centre, says we still need to push for a vaccine. HPTN 052 and PrEP are “powerful tools that can prevent new HIV infections and must be appropriately and aggressively implemented,”

he told Nature.

The implementation of PrEP will present several challenges though, he added. Giving powerful drugs to otherwise healthy people is not without ethical issues, and prophylactic treatment will need to be meted out carefully to guard against the development of resistance. Starting antiretroviral treatment early, as the HPTN trial suggests, is still hindered by the fact that existing tests are not sensitive enough to detect very low CD4 counts.

“Ultimately, an effective HIV vaccine would be simpler to give and protect more durably against infection. Vaccines are also among the most cost-effective of medical interventions. An effective AIDS vaccine will therefore remain an invaluable weapon in combating the spread of AIDS,” said Nabel.