The HIV world was jumping, if not jittery, last week, with a third case of HIV pre-exposure prophylaxis (PrEP) failure reported, this time, at CROI 2017. Notable was that it did not involve drug–resistance, the cause of the previous two widely reported PrEP failures, including one occurring in Toronto. In fact the reason for PrEP failure in this latest case, a 50-year old gay man from the Netherlands, a heavy drug user who was extremely sexually active - and there may be some clues there - remains a question for scientific debate.
Want to know more? The case is particularly complicated. For a full review of the circumstances go here .
Inevitably the suggestion has been raised on Facebook and elsewhere that PrEP failures point to the unreliability of undetectable viral load as a prevention method. In fact I have heard colleagues who work is gay men’s sexual health tell me that PrEP failures are why you cannot say Undetectable = Untransmittable. a message which even the International AIDS Society and many others, including CATIE, support.
Frankly that’s a fallacious argument that needs to be shot down.
Simply put PrEP and treatment as prevention (TasP) are two entirely different animals. Comparisons between the differing results of the two make no sense.
One more time . . PrEP is a regime for people who are HIV-negative. Nobody has ever said PrEP is 100% safe – in fact Gilead, the manufacturers of Truvada, recommend it be used in combination with condom use. “Nevertheless PrEP appears to be nearly 100% effective if taken consistently so that there are high drug levels in the body at the time of exposure to HIV” says aidsmap.
In contrast, the use of ART to maintain an undetectable viral load in people living with HIV works to reduce levels of virus in the blood to such low levels that the virus cannot be transmitted sexually. There have been no transmissions in carefully monitored studies involving individuals engaged in condomless sex with discordant partners.
It’s apples and oranges. The experience of negative individuals using Truvada as a prevention method tells us absolutely nothing about the efficacy of Truvada or any other drugs alone or in combination in individuals who are already HIV-positive. Period.
The best one can surmise is that frequency of sex is in itself a risk factor when using prevention methods, including condoms, which are not 100% effective. Explains aidsmap “A clue may lie in the fact that the man had a lot of high-risk sex, even for someone enrolling in a PrEP trial. During his first seven months in the study he averaged 56 anal sex partners per month and about 30 episodes of condomless sex a month. He averaged 16 days per month when he did have condomless sex and on those days averaged 3.7 partners. “ (There were other factors involved in this case which were untypical too, so drawing conclusions as to what went wrong is particularly difficult.)
Said Gus Cairns on Facebook recently “There's no specific hypothesis as to what happened but the person who caught HIV, despite high PrEP drug levels, was having a LOT of sex and perhaps there is simply a statistical chance that PrEP will fail in one in thousands of exposures, and this is the case. NB this has no bearing at all on the likelihood of the opposite case - of transmission from someone who is on fully suppressive ART. There, there is essentially no HIV to transmit. Here, there's lots of HIV and a drug barrier that once in a blue moon HIV may be able to sneak through.”
And by the way – there is a happy ending of sorts: once diagnosed the Amsterdam man was placed on ART immediately on diagnosis and achieved an undetectable viral load after one month. Good for him.