Vaccine in Imbokodo Study Fails to Provide Protection

Phase 2b HIV Trial Vaccine Fails

Preliminary analysis of the Imbokodo study of an experimental HIV vaccine demonstrated that the vaccine did not provide sufficient protection against transmission of HIV. The preliminary analysis, conducted by an independent data and safety monitoring board, concluded that the study in a population of at-risk young women in sub-Saharan Africa, did not meet its goal, with results falling short of statistical significance. Thus, the Imbokodo study has been discontinued, although further analysis continues.

Begun in 2017, the Imbokodo study reached full enrollment in 2019, and completed vaccinations in June 2020. The study evaluated the experimental regimen in approximately 2,600 women between ages 18 and 35 across five countries—Malawi, Mozambique, South Africa, Zambia and Zimbabwe—where, according to UNAIDS, women and girls accounted for 63% of all new HIV infections in this region in 2020.

The study’s primary endpoint was based on the difference in number of new HIV transmissions between the placebo and vaccine groups from month seven (one month after the third vaccination timepoint) through month 24. This data found that through 24 months of follow up, 63 participants who received placebo (4.32% incidence) acquired HIV, compared to 51 participants who received active vaccine acquired HIV (3.61% incidence). This analysis demonstrated a disappointing vaccine efficacy of only 25.2% (95% confidence interval of vaccine efficacy -10.5% to 49.3%).

Participants in this Phase 2b proof-of-concept study who acquired HIV will be referred to high-quality treatment and care.

“The high rates of HIV acquisition seen in the Imbokodo study of young women in sub-Saharan Africa remind us that, despite great progress made in treatment and prevention, HIV remains a huge health challenge for the region,” Glenda Gray, Protocol Chair and Co-Principal Investigator and Director of HVTN Africa Programs and President & CEO of the South African Medical Research Council said in a press release. “This underpins the need to apply the knowledge gained from this trial to continue to advance the pursuit of a global HIV vaccine.”

Although the Imbokodo study has been discontinued, the Phase 3 Mosaico study, or HVTN 706/HPX3002, is testing the safety and efficacy of an “optimized” experimental vaccine regimen in a different population and in different areas of the world.

—Reporting by Hank Trout


Hank Trout, Senior Editor, edited Drummer, Malebox, and Folsom magazines in the early 1980s. A long-term survivor of HIV/AIDS (diagnosed in 1989), he is a forty-one-year resident of San Francisco, where he lives with his husband Rick.