Since the dawn of HIV epidemic in 1981, the development of an HIV vaccine to protect people from infection has been a priority for many scientists. However, there have been many challenges to developing a vaccine. For example, HIV mutates rapidly to evade immunity, and there are no recovered HIV/AIDS patients, so an immune response induced by a vaccine cannot mimic that of a natural recovery.

Still, there is promising progress being made.

Recently, scientists tested different vaccine combinations on monkeys using a prime-boost approach, where one vaccine is given as a priming dose, and a booster shot is administered 6 months later. To mimic vaccines that would be used in humans, the SIV strain (SIV is the monkey analog to HIV in humans) used to make the vaccines was different from the strain used to infect the monkeys. The SIV strain used for infection was chosen to be particularly difficult to develop vaccines for, because it is resistant to developing neutralizing antibodies. Only neutralizing antibodies can protect against infections, like HIV, that attack the immune system.

This study was the first to show that vaccines that can protect against infection by a neutralization-resistant SIV, and the study showed that the Env surface protein on HIV is an important ingredient in developing a successful vaccine. Compared to sham controls, one vaccine combination in the study reduced the chance of becoming infected per viral exposure by 80%.

One of the successful vaccine combinations is now being developed for early-stage clinical trials in humans.

D Barouch et al., Vaccine protection against acquisition of neutralization-resistant SIV challenges in rhesus monkeys. Nature DOI: 10.1038/nature10766 (2012).