Vaginal Bacteria Can Change Efficacy of Tenofovir in Preventing HIV Infection

The composition of the vaginal microbiome impacts the efficacy of tenofovir to prevent HIV, a new study found.

Although tenofovir has a high success rate in HIV prevention among high-risk men, its efficacy varies among women.

In study published in Science, investigators sought to examine the role of the vaginal microbiome in the efficacy of tenofovir.

They used samples obtained from a subset of 688 participants in a clinical trial evaluating the efficacy of tenofovir intravaginal gel in HIV prevention among South African women, some of whom went on to contract the virus.

The investigators identified 2 major vaginal bacterial compositions in the samples: 1 was dominated by the bacteria Lactobacillus and the other by Gardnerella vaginalis.

The results of the study showed that tenofovir was 3 times as effective in protecting against HIV infection among women with a Lactobacillus-dominate vaginal microbiome compared with women who did not.

Among women where Lactobacillus predominated, tenofovir reduced HIV incidence by 61% compared with only 18% in women with non-Lactobacillus bacteria.

High HIV acquisition was observed among women who had dominant Gardnerella vaginalis because the bacteria could rapidly metabolize, and ultimately, inactivate tenofovir.

“The vaginal microbiota is yet another variable that we have to take into account when we are thinking about why one intervention does or doesn’t work,” co-author Khalil Ghanem told Science News.

The authors noted that their findings serve as a reminder that developing successful interventions that optimize and improve the health of women will remain out of reach without a deeper understanding of the function, dynamics, and structure of the vaginal microbiome.

“This study tells us that when we are thinking about vaginally delivered medications, we may need to think about the vaginal microbiome as well,” commentary coauthor Susan Tuddenham told Science News.

Additionally, women could be following the directions of vaginal medications to a T but “still not get the full benefit of that medication,” Ghanem added.