A large trial for a vaccine against the HIV virus, which is responsible for AIDS, started in South Africa in late 2016. The study is officially called HVTN 702, or Uhambo.
The vaccine requires 5 injections within a year, then researchers will follow up for the following two years to test whether the vaccine regimen works. Results for the vaccine study are expected by 2020.
If the vaccine meets the 50 percent threshold, it will be considered sucessful and this question will be resolved as "Yes".