Picture: 123RF / KTSDESIGN
Picture: 123RF / KTSDESIGN

An experimental HIV vaccine first tested in Thailand has triggered a surprisingly strong immune response in South African volunteers, though the region is home to a different strain of the virus, research published this week in the international peer review journal, Science Translational Medicine, shows.

SA has the world’s highest HIV burden with more than 7-million infections, which are dominated by clade C infections. In Thailand, the dominant strains is clade B.

The study results challenge the idea that each region of the world needs its own type of vaccine, tailored to the local strains of HIV, said Glenda Gray, the study’s principal investigator and president of the Medical Research Council.

The Thai RV144 vaccine was the first experimental HIV shot to demonstrate modest protection against the virus, but its efficacy waned more than time. A vaccine that offers even partial protection against HIV could be useful, so scientists tested the safety and efficacy of the same vaccine in 100 South African volunteers in 2013 in a phase 1b clinical trial called HVTN 097.

Preliminary analysis of the results, presented at a conference in Cape Town in 2014, found South Africans mounted an equally good immune response as Thais. Now, a closer look, with new and better tools, has revealed that the vaccine in fact elicited a stronger immune response at the cellular and antibody levels in the South African volunteers.

“This study shows cross-clade activity and immune responses that we didn’t expect,” said Gray.

The results are important, she said, as HVTN  097 was a precursor to another study under way in SA called HVTN 702, which used a modified version of the Thai RV155 vaccine that is clade-C specific.

As in the Thai study, the immune responses in the volunteers enrolled in HVTN 097 diminished more than time, suggesting that booster shots could help maintain its efficacy, said Gray.

The vaccine was also found to be equally effective among fat and thin volunteers, an important consideration in SA where a significant portion of the population is overweight. A previous clinical trial called HVTN 503, or Phambili, found a weaker immune response among people who were overweight.

The HVTN 097 trial was supported by the US National Institute of Allergy and Infectious Diseases.