A study of 657 people taking PrEP, the daily pill that can prevent HIV, has found that not a single person contracted the potentially deadly virus over two and a half years of observation.
The research showed that despite rising rates of STIs in the group, as well as a decline in condom use, the pill was able to protect everyone involved from HIV. The study was conducted by doctors from Kaiser Permanente, a managed care company based in Oakland, California.
"What our study shows very reassuringly is that PrEP works in a real world setting," said lead researcher Dr. Jonathan Volk of Kaiser Permanente San Francisco Medical Center. "HIV prevention in 2015 is very exciting because we have several tools that are available for reducing risk, and PrEP is one of those tools."
PrEP, which stands for preexposure prophylaxis, is sold under the brand name Truvada. It has been on the market for HIV treatment since 2004, but wasn't approved by the FDA for HIV prevention until 2012. However, a survey of half of America’s pharmacies found that only about 3,000 people had begun taking it as of March 2014, as opposed to the half-million Americans the pharmaceutical company estimated would be good candidates for the drug.
Volk's finding is significant because it comes from one of the first “real word” studies of PrEP use, as opposed to clinical trials. The researchers hope that while the drug seems to be well-known to the gay community (99 percent of study participants were men who have sex with men), more work needs to be done to reach other high-risk men and women including transgender people and injection drug users.
"Interest in PrEP in our experience has been lower among those groups, and we want to make sure we’re reaching all individuals who are at risk for HIV," said Volk. "When you look at who is getting infected with HIV, we still have work to do."
Volk and his team recruited 657 people who were interested in taking PrEP as part of the study. They measured the participants at baseline for HIV and other STIs, and then checked up on them again every three months.
Volk notes that based on data from a different PrEP trial with a similarly high rate of STIs, he would have expected an HIV rate of 8.9 cases per 100-person years in his cohort. Instead, the HIV incidence rate was zero.
Some HIV/AIDS experts are critical of Truvada, arguing it promotes irresponsible sexual practices and may be responsible for declining condom use and rising rates of other STIs. Indeed, Volk’s study found that after six months of PrEP use, 30 percent of participants had at least one STI, ranging from chlamydia to gonorrhea and syphilis. After 12 months, that percentage increased to 50 percent of participants.
Additionally, 188 PrEP-using participants also responded to a survey about their sex lives six months into taking the drugs, and reported that while most didn’t change the number of sex partners they had, 41 percent did decrease their condom use.
However, Volk emphasized that this behavioral data isn’t rigorous enough to establish a causal link to Truvada use. For instance, this data doesn’t assess HIV risk of the participant or their partners, and it doesn’t take into account whether people are “PrEP sorting” -- choosing to forgo condoms if their partner is also taking PrEP. And, of course, there’s no control group to assess how PrEP did or didn’t change people’s sexual choices.
"Without that more nuanced understanding of when and how people are using condoms, it’s really difficult to make those determinations,” he said.
One limitation of Volk’s study is that it took place in San Francisco, a city with higher rates of HIV than others in the U.S. This means there are also higher rates of HIV treatment and thus viral undetectability, and Volk suggests that his findings may not be generalizable to other cities.
"It really extends the very impressive evidence we have from randomized controlled trials and demonstration projects and provides us with very exciting news: that this medication can be delivered effectively in a real world setting,” Volk concluded.
Volk’s research was funded by a Kaiser Permanente community benefits research grant and published in the Oxford journal Clinical Infectious Diseases.