Study reports the results of a successful phase 1/2a human trial of a new HIV vaccine across several continents and nearly 400 subjects. The trial used a new approach, testing seven different vaccine formulations in subjects around the world. After giving subjects four doses over one year, the researchers homed in on one particular formulation that seemed to display the greatest anti-HIV immune response. The vaccines were all declared safe for human administration, with only five relatively mild adverse events reported across the entire safety and efficacy trial.

In a related study with rhesus monkeys, the vaccine formulation that was the most successful in humans also displayed great responses in animal experiments. Around two-thirds of the animals displayed complete immunity to SHIV (the simian form of HIV) after six attempts at infection.

The challenge at this stage is to replicate these results in broader human cohorts, and prior work has demonstrated a frustrating inconsistency in moving from primate experiments to human trials. The next stage will be key in revealing whether this is the vaccine breakthrough we’ve been waiting for, or whether this will be relegated to the growing pile of failed attempts. The upcoming phase 2b trial will take place in southern Africa and encompass 2,600 women designated at-risk for contracting HIV.

Dan Barouch from Harvard Medical School, and one of the researchers leading the prior successful vaccine trials, does urge caution, suggesting that the challenges faced in developing an effective HIV vaccine are unprecedented and excitement should be moderated until this phase 2b trial demonstrates efficacy.

“We eagerly await the results of the phase 2b efficacy trial called HVTN705, or ‘Imbokodo’, which will determine whether or not this vaccine will protect humans against acquiring HIV,” says Barouch.