People who take pre-exposure prophylaxis (PrEP) after contracting the virus may experience a delay before HIV tests detect the virus, Reuters Health reports. However, this delay is not associated with an increased risk of the virus developing resistance to the medications in Truvada (tenofovir disoproxil fumarate, or TDF/emtricitabine).

Furthermore, there is an apparent benefit to being on even just a partial antiretroviral (ARV) treatment regimen during early infection: a reduction in viral load, and therefore infectiousness, and a delay in progression of very early HIV disease.

Standard HIV treatment requires three or more ARVs at a time to fully suppress the virus. Truvada contains only two ARVs.

Publishing their findings in the journal AIDS, researchers analyzed data from the Partners PrEP Study, a randomized placebo-controlled trial conducted among men and women in Kenya and Uganda, looking for those who had contracted HIV during the trial. The participants were randomized to receive Truvada or Viread (TDF) as PrEP or a placebo. This trial was conducted before researchers determined that the two drugs in Truvada, emtricitabine and tenofovir disoproxil fumerate, or TDF, were preferable for use as PrEP compared with the one drug in Viread, TDF.

Scientists estimate that when Truvada is taken daily it reduces the risk of contracting HIV by 99 percent or more among men who have sex with men (MSM) and 90 percent or more among women. (The risk reduction for women may very well be greater than 90 percent, but there isn’t sufficient research available to refine the estimate.)

Some people entered PrEP studies having contracted HIV very recently before enrolling and therefore testing false negative before starting PrEP. (A negative HIV test is required before starting PrEP.) Others likely adhered poorly to the daily drug regimen or took no drug at all before contracging the virus. In real-world practice, there have been three cases of individuals contracting HIV—in two cases they contracted highly drug resistant strains—while apparently adhering well to the PrEP regimen. These cases all involved extenuating circumstances that collectively indicate such cases of PrEP failure will likely remain rare.

Participants in the Partners PrEP study were seen monthly and provided HIV rapid testing along with a month’s supply of medication. Those whose rapid tests indicated a positive or indeterminate result then received a more sensitive third-generation EIA test for HIV at a local lab.

The researchers stored plasma and serum samples from the participants at their one- and three-month visits and then every three months after that, as well as at any visit at which a rapid test indicated a possible HIV infection. For those who contracted the virus, blood samples were stored from the visit when they tested positive and then one month later and quarterly after that.

Those who had a positive or indeterminate result on their rapid HIV test were temporarily taken off PrEP. If the EIA was positive, they were taken off PrEP permanently.

The researchers defined a delay in detecting a new case of HIV as more than 100 days between an individual providing the first sample that sensitive testing later identified was infected with the virus and the first detection of the virus through a rapid test.

A total of 138 people were confirmed to have contracted HIV during or just before the study, including 71 in the placebo group and 67 in the active PrEP arm, including 40 who received Viread and 27 who received Truvada.

Fifteen of these individuals likely contracted the virus just prior to entering the study, while 111 contracted the virus during the study. Nine contracted the virus during a period when for programmatic reasons they were off study drug and three contracted the virus at the point when the placebo phase was canceled and everyone was offered active PrEP.

Those who received active PrEP were 3.49 times more likely to experience a delay in detection of their infection. However, such a delay was not associated with an increased risk of the virus developing resistance to the drugs in Truvada and Viread.

The participants who took PrEP after contracting HIV also progressed more slowly through the very early stages of infection, known as the Fiebig stages. Hitting Fiebig stage V took 28 days among those on PrEP compared with 17 days among those in the placebo arm. After adjusting the data to account for differences in Fiebig stages, the researchers found that individuals’ viral load was about 88 percent lower (2/3 log) among those in the PrEP arm compared with those in the placebo arm.

The researchers concluded that more sensitive HIV tests are necessary to detect infections earlier in people receiving PrEP.

A major upside of taking Truvada as PrEP after contracting the virus is that the drug will reduce a person’s viral load by as much as 1,000-fold, making him or her vastly less infectious.

At the recent 9th International AIDS Society Conference on HIV Science in Paris (IAS 2017), researchers reported a case study of a man who contracted the virus days before staring PrEP who was put on a full HIV treatment regimen after seven days of Truvada use. He was later taken off ARVs entirely and spent seven months in a state of viral remission before his viral load rebounded and he was put back on treatment for the virus.

To read the Reuters Health article, click here.

To read the study abstract, click here.