Treatment as Prevention

There was some great news this week in a new way to prevent HIV transmission.

A massive study of over 1700 couples around the world found that treating someone with HIV can protect their partner from getting infected.

96% effective

The study, done by the HIV Prevention Trials Network found such a strong effect (96% effectiveness!) that the trial was actually ended early – a step that isn’t often taken.

The trial, called HPTN 052 began over 6 years ago in April 2005, and was slated to run until 2015. The couples enrolled in the trial were what the HIV field called “serodiscordant couples”, meaning they had different HIV (sero)statuses. One partner had HIV, and the other partner was negative.

These couples were recruited from 13 sites around the world – mostly Brazil, India, Thailand and Sub-Saharan Africa. As with most clinical trials, the participants were randomized to the different “arms” of the study. In this case, either:

1)    The positive partner started antiretroviral therapy right away


2)    Wait until their CD4 T cell count fell below 250 cells per cubic millimeter before starting treatment

The main objective of the study was to track if the number of HIV infections in the first group was lower than the number in the second group.

In the study, there were 39 partners who got infected, but only 28 of these were actually genetically linked to the partner (i.e., they probably got infected with a virus from someone else). Of these 28 documented cases of HIV transmission, only 1 was in a couple where the positive partner was on antiretroviral therapy. That amounts to a 96% effectiveness of therapy in preventing HIV transmission to a sexual partner.

Most clinical trials have a separate “Data and Safety Monitoring Board” that meets to look at the data while the trial is still running. The idea of the DSMB is that they are independent, so they don’t necessarily “care” how the trial turns out. And if they find that there’s no difference between groups in the trial (indicating that the intervention being tested doesn’t work), OR that there’s such a huge difference between the groups in terms of safety or effectiveness, then the DSMB may choose to stop the trial early. Basically, when a DSMB stops a trial early, it’s either because of really bad news or really good news.

In this case, they met, saw the 96% reduction in infection (good news, of course!), and halted the trial almost 4 years early.

Other Treatment as Prevention Research

There have been indications before that an approach like this might work, but they’ve mostly been “observational” studies that are only able to show associations instead of definitive, scientific proof that treatment as prevention works.

The idea is that people with lower viral loads are less likely to transmit their HIV to someone else, and since treatment knocks the viral load down to “undetectable” levels, then treatment might do the same thing.

Here in BC, researchers at the BC Centre for Excellence in HIV/AIDS showed that increased “coverage” of antiretroviral therapy meant that more people HIV had lower viral loads. This was associated with an overall decrease in new HIV diagnoses by over 50%.

Another study in San Francisco saw a similar trend. They looked at the overall level of “community viral load” (the blue bars), which is the viral loads of all individuals measured with HIV and averaged out over the whole community.  This gives a rough idea of “how much” HIV is in the community. The height of the blue bars for community viral load was associated with the red lines for new cases of HIV.

Coincidentally, there was a workshop on Treatment as Prevention here in Vancouver, just last week – right before the results of HPTN came out. If you’re interested, all of the talks are posted on YouTube, and they give a great run-down on the approach.

Even before the HPTN 052 results came out, the studies up to that point were pretty convincing that treating people with HIV can prevent infections in their partners.

In fact, in BC, our treatment guidelines say that people are eligible for earlier antiretroviral treatment if they are in a serodiscordant couple and want to protect their partner from becoming positive themselves. Earlier therapy has also been found to be associated with a lower risk of death  compared to starting later. So starting treatment early can be good for our own health, as well as the health of our partners.

And now we have definitive proof from HPTN 052 that treatment as prevention works.


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