The HIV vaccine, known as HVTN100, will be trialed in South Africa later this year, after preliminary testing showed promise.
The experimental vaccine came after a 2009 trial in Thailand called RV144. This was the first major success, after years of struggling to invent a vaccine. One year after the 2009 tests, the effectiveness of RV144 was evaluated at 60 percent. However, after 3.5 years after the vaccination tests, the effectiveness reduced to some 31 percent, leading researchers to a new goal: raise the effectiveness of a vaccine back to a 60-percent minimum, and keep it there.
"The obvious question is: Can we now replicate those results and can we improve upon them with greater breadth, depth and potency?" asked Anthony Fauci, director of the National Institutes of Allergy and Infectious Disease, whose organization is sponsoring the research.
The earlier vaccine was modified and an adjuvant was added, to boost the body's immune response. Researchers also modified the vaccine to handle a particular strain of HIV endemic to the African continent.
According to Linda Gail Bekker, deputy director of the Desmond Tutu HIV Centre in Cape Town, South Africa, and president-elect of the International AIDS Society, who is leading the vaccine trials, four criteria were set as measures of the HVTN100 vaccine's likely effectiveness, including the level of T-cell and antibody response to fight the virus if it were to infect, and the trial gave a "tick on all four."
Some 250 participants took part in the 2015 preliminary HVTN100 test. This year the vaccine will be tested on 5,400 people, across four cities in South Africa, and continue for three years.
"We're hoping this can be the first licensable vaccine regimen in the world," said Gail-Bekker. "We are ultimately going to need a vaccine to shut [the HIV epidemic] down."
Researchers caution, however, that a vaccine alone won't be enough to provide protection against the disease, but is intended to be effective alongside existing safeguards, including prevention, treatment and social intervention.