06/13/2013 01:08 pm ET Updated Feb 02, 2016

Undetectable Viral Load: As Safe as It Sounds?

The past four weeks have seen the 30th anniversaries of two milestone events. In mid-May 1983, the booklet How to Have Sex in an Epidemic was published, and two weeks later the Denver Principles were drafted. Decades later, gay men continue to explore possibilities around HIV prevention; the epidemic also continues. Dr. Joseph Sonnabend, a physician and AIDS researcher and co-author of How to Have Sex in an Epidemic, shares his thoughts on the pros and cons of one of the latest approaches.

Mark Adnum: In terms of the risk of transmission of HIV, what does it mean if someone is "undetectable"?

Dr. Joseph Sonnabend: In the context of transmission risk, "undetectable" generally refers to a failure to detect HIV in the blood stream. "Undetectable" does not mean it's not there, but that it can't be found by a particular test.

There is a relationship between viral load and transmission probability, which falls as viral loads decrease. This is evident from studies on populations. In principle this should also be the case on an individual level, but here there are some practical considerations.

For example, the significance regarding transmission of a single undetectable viral load three months ago, or even yesterday, is uncertain. Since we can't know the viral load at the time of sex, we would need additional information; being undetectable without qualification may not be enough information to make a choice about unprotected sex. In 2008 Swiss researchers suggested a set of circumstances under which an individual with an undetectable viral load might be considered to be incapable of transmission. According to them, HIV-infected individuals on effective suppressive antiviral treatment who had undetectable viral loads for at least six months and who had no sexually transmitted infection could be considered to be non-infectious. This view was certainly not shared by everyone.

Maybe much of the problem is in the wording: An assurance of zero risk is just not attainable. I do essentially agree with the idea behind the Swiss statement -- at least to the extent that it's possible to define circumstances where the probability of transmission is extremely low -- even if it's not possible to precisely quantify, and allow individuals to make an informed decision.

Given that the receptive partner is at greater risk, their best protection is of course to refuse sex with a partner who will not use a condom. Among men who have sex with men, there surely can only be very limited situations when the receptive partner would choose the more dangerous course. We should also make clear what we know about risk, and provide more information than simply relative risk reduction numbers.

Adnum: Why, then, do you think that "undetectable" is being promoted by some as an addition to the safe-sex toolkit, and by others as an alternative to condom use altogether?

Dr. Sonnabend: If in fact an undetectable viral load is being promoted as a new alternative form of safe sex for all, it must be coming from a very small group of people, and I suppose one could speculate on what motivates them -- maybe it's just ignorance -- if they are making a general recommendation. But I would also agree that there are some circumstances when reliance on a known and established undetectable viral load would be reasonable, although I think these would be relatively uncommon.

The consistent use of condoms is the most effective means we have to prevent sexual transmission of HIV. It has a track record unmatched by any other prevention modality. Those promoting various forms of what are now called biomedical prevention generally agree, but then almost invariably go on to say that people just don't use condoms consistently. They apparently have come to the conclusion that prevention education does not and cannot work, with a confidence that's remarkable, because there has been so little experience of well-targeted prevention education. If prevention education has been a failure, it's because we have not provided it well enough.

Properly targeted prevention education has never received much support, and with biomedical prevention -- that is, prevention by drugs -- being promoted so vigorously, it's likely that what little support there's been may completely dry up. Of course we should study new prevention modalities, but in doing so we should strengthen prevention education. With budgetary constraints, support for prevention education may dwindle even further as the burden to pay for prevention shifts to individuals and entities that purchase drugs, such as insurers, private or governmental.

We have known where to target prevention education almost from the beginning of the epidemic. It will remain for a future generation to attempt to understand why both governmental authorities responsible for protecting public health as well as communities most affected did not respond adequately.

Whatever the explanation, it will have to also include the fact that early on, we knew that highly targeted prevention education, when crafted by the communities at greatest risk, can work. This was demonstrated in the earliest years of the epidemic in San Francisco and New York City. The earliest prevention activities that promoted condom use by gay men emanated from individuals within the communities most affected, with absolutely no governmental or organizational support. How to Have Sex in an Epidemic, the first booklet that promoted the use of condoms, was self-published and distributed 30 years ago in New York, paid for by a donation from a single individual, Randall Klose, supplemented by an IRS tax refund to Michael Callen, one of the authors. (Another author was Richard Berkowitz.)

Adnum: So at all times, it would be sensible to interrogate the facts and figures rather than uptake them without edit and let them inform your behavior?

Dr. Sonnabend: You don't need a technical training to be able to understand that the evidence that supports a particular contention or recommendation can vary in strength. You certainly don't need to be an expert yourself to know that a recommendation based on the opinions of a particular group of experts is not as reliable as one based on the results of well-designed and executed clinical trials.

Of course, it's the researcher's job to generate figures and suggest explanations, but we should not just simply accept their pronouncements without question, as if science were a faith-based enterprise.

Anyway, there is absolutely no reason to simply accept that the interests of researchers necessarily coincide with the best interests of people with and at risk for AIDS. There is a great quotation by Oliver Wendell Holmes from 1860:

The truth is that medicine, professedly founded on observation, is as sensitive to outside influences, political, religious, philosophical, imaginative, as is the barometer to the changes of atmospheric density.

In other words, researchers are susceptible to political, religious and philosophical influences despite claims of objectivity. This was restated by René Dubos a century later, who in Man Adapting wrote that the presuppositions on which medicine operates are influenced by prevailing social attitudes (and prejudices). This just reminds us that scientists, although professedly dealing with objective issues, are also people whose personal views can be as varied as those of the population at large.

Scientists are no different to anyone else; our expectation that scientists might be immune to distorting influences is mistaken. Biomedical prevention, particularly pre-exposure prophylaxis and reliance on an undetectable viral load achieved by effective treatment to prevent transmission, are nowhere even close to being ready for general use. There is a place for these modalities in rather rare, specific situations.

Condoms work. This is the straightforward and easily understood message that should constantly be heard from research and community leaders. This is most especially true when they speak of biomedical prevention in the form of PrEP and treatment as prevention.

That research and community leaders do not do this undermines the use of condoms with the false and dangerous impression that biomedical prevention is an alternative prevention modality.

There is a place for biomedical prevention, and we might expect research and community leaders to clarify what these unusual circumstances are. For example PrEP is a rational harm reduction approach to those who will not use condoms.

For most, the use of condoms remains the most reliable means to prevent the sexual transmission of HIV. Community activists should surely demand that prevention education targeted to those who need it most be well-funded and well-done. This is something that can definitely help to prevent new infections, and deserves greater enthusiasm than that shown in their support for biomedical prevention.