Spotlight Center on HIV Prevention Today


HIV Undetectable Does Equal Uninfectious: The Swiss Statement and the Vindication of Pietro Vernazza

October 7, 2016

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Pietro Vernazza, M.D.

Pietro Vernazza, M.D., at his induction into the Love Superhero Hall of Gratitude for work on safer conception options for HIV affected couples (Credit:

On Jan. 30, 2008, Pietro Vernazza, M.D., was on vacation with his wife, Eva, in the Swiss Alps when his phone rang.

It rang again when they got back to their hotel room, and then again the next day. The whole week was taken up with one call after another. When he returned home a few days later, he appeared on Swiss national radio. Days after that, he began what turned into a worldwide tour of public health and professional organizations. By October, he was at the U.S. Centers for Disease Control and Prevention (CDC), answering the same questions he'd been answering for nearly a year: What were you thinking? How could you say that? Where's the data?

What he'd said, in a statement in the Bulletin of Swiss Medicine, was this: If you're a person living with HIV on consistent antiretroviral treatment (ART), if your viral load has been undetectable for at least six months, if continuing testing shows that your viral load continues to be undetectable, and if you don't have other sexually transmitted infections (STIs), you don't need to use condoms during sex.

You cannot, the statement said, pass on HIV.

This was the Swiss Statement, a public policy salvo lobbed into the heart of the HIV world -- one that prompted a swift and intense backlash. People called it premature. People accused Vernazza of getting ahead of the science. Some demanded he produce data to prove there had been no transmissions. Others simply called him irresponsible.

But it's not 2008 anymore.

"The Swiss Statement, when it first came out, I thought it was outrageous," said Seth Kalichman, Ph.D., an HIV researcher at the University of Connecticut. "The Swiss Statement isn't outrageous anymore."

Indeed, nearly nine years later, it's more than a statement. It's a fact, backed up by gold-standard studies released at the Conference on Retroviruses and Opportunistic Infections (CROI) and the International AIDS Conference (IAC).

"The evidence base has grown," said Jared Baeten, M.D., Ph.D., a University of Washington researcher who has been studying HIV prevention for more than a decade. "Now it backs up the Swiss Statement."

This is the story of how the Swiss Statement went from policy pariah to documented fact. And it is the story of the vindication of Pietro Vernazza.


Entering the Antiretroviral Treatment Era

The concept of lower levels of virus in the blood leading to lower rates of transmission is a truism in biology.

But in 1993, we were still two years away from the U.S. Food and Drug Administration approving the first protease inhibitor drugs that ushered in the new era of antiretroviral treatment. Americans with HIV were dying, often quickly, and there was no way to stem the tide of the virus in the blood and cells of people who'd acquired it.

Back then, Vernazza -- at the time a post-doctoral fellow at the University of North Carolina (UNC) -- wasn't concerned with lowering transmission rates. He was studying something far simpler: whether you can determine if a man living with HIV is infectious by measuring his semen.

But then, protease inhibitors came out, and scientists started to ask a different question: If treatment could reduce viral load -- that is, the amount of HIV in the blood and genital tract -- might there be literally nothing for them to pass on? Might they be functionally uninfectious?

In a 1999 paper in the journal AIDS, HIV researchers at UNC, including Vernazza, Joseph Eron, M.D., Susan Fiscus, Ph.D., and Myron "Mike" Cohen, M.D., tried to figure out the likelihood that someone living with HIV would pass on the virus during sex.

It was a puzzle. Not every form of transmission was as effective at spreading the virus, the team wrote in AIDS. Mother-to-child transmission was highly efficient and so was blood transfusion. But sex? That, the UNC researchers said, "is less efficient and highly variable."

The challenge wasn't just that some people seemed to replicate HIV more slowly than others, meaning there was less of it in their body. It was also that some HIV treatments seemed to work better than others at suppressing viral load. Some, such as zidovudine (AZT, Retrovir), had been found to reduce mother-to-child transmission of HIV even when treatment started late in pregnancy -- a promising development. But other drugs weren't powerful enough to reduce transmission, the paper said. And the data that did exist seemed to indicate that drugs that could lower the virus in the blood weren't always successful in doing so in semen and vaginal fluid.

"Patients need to be carefully informed about the significance of treatment induced reduction of genital shedding of HIV," the paper stated. "Reduced infectiousness does not equal lack of transmission and more importantly, not every antiviral treatment does result in reduced infectiousness. In order to be effective on a public health basis, reduced infectiousness must be coupled with continued safer sex practices."

In other words, condoms. In practice, what this ended up meaning, Vernazza said recently, is that doctors didn't talk at all about the power of treatment to reduce transmission.

"We had prevention campaigns and ads all over the streets, on TV, saying condoms, condoms, condoms," Vernazza said. "That was a campaign from the '80s that had just been maintained over all these years."

HIV Equipoise

But by 2003, Vernazza was starting to feel differently.

By this time, he had finished his post-doc work in North Carolina and had taken a job as the chief of the Division of Infectious Diseases at the Cantonal Hospital in St. Gallen, Switzerland. There, he was working with a very specialized group of people living with HIV: straight people on treatment who wanted to have children with their HIV-negative partners.

A survey of all the patients who were part of the Swiss HIV Cohort Study, an ongoing national study of Swiss people living with the virus, found that about one in five or six were not using condoms. And that was only what people were willing to tell their physicians; an anonymous questionnaire sent out later found substantially higher rates of condomless sex.

Even if only one in four people with HIV on treatment were having sex without condoms, they should be seeing their partners' acquiring HIV, Vernazza said. But they weren't.

"Out of 8,000 patients, we did not see reports of transmissions to a partner," he said. "So we knew the risk must be low. And when we interviewed these HIV-discordant couples, very uniformly they told us about their assumption of a very high risk of transmission despite very long and stable HIV-RNA suppression in the infected partner. Because of the wrong information they had, they did not conceive children even though they wanted to."

For Vernazza, it was an ethical dilemma. In the world of medical ethics, it's called equipoise: If a clinician sees two options as equally valid, he is ethically obligated to offer all treatments to his patients and let the patients decide. For example, if the couples you're working with really want to have children and using condoms is prohibiting this, and if treatment is preventing the partners who are living with HIV from passing on the virus, the couples might need to be told. To do otherwise, he said, would unnecessarily force a hardship on those couples' relationships.

He knew talking to patients would go against everything public health campaigns said about preventing the spread of HIV. When I spoke to Vernazza in 2011 for my book Positively Negative, he told me, "There's a belief that [we] should not tell."

Indeed, in practice, people living with HIV were getting the opposite of equipoise. Doctors were telling patients the risk of transmission was real, even though, Vernazza said, "none of us in the whole medical field had ever seen a single case of transmission under these circumstances." Add in the fact that other public health recommendations -- such as those regarding the negligible risk of HIV transmission via kissing -- were based on far smaller samples of people (100, by Vernazza's estimate) and Vernazza said he felt compelled to speak up.

"We felt we needed to tell them: 'Listen, the risk of transmission is not as high as you assume,'" he told "In fact, it's probably zero."

He started to roll out the options with his patients that year and the next -- offering, in addition to timed, condomless sex for conception, an HIV prevention pill before and after sex for the HIV-negative partner (an approach now called pre-exposure prophylaxis or PrEP). The couples who took him up on it were carefully monitored, including counseling and treatment for STIs and regular viral load monitoring.

Many had babies. No one got HIV.

By 2008, he and his colleagues on the Swiss Federal AIDS Commission, of which he was now the president, were ready to roll this out as policy for the rest of Switzerland's HIV doctors.

He got together with physician groups, public health policy officials and legal experts and drafted guidance meant for Swiss physicians only. It laid out the current research: two observational studies, along with the mathematical model he had contributed to at UNC, and the experience of the Swiss HIV Cohort. On Jan. 30, 2008, it was published in the Bulletin of Swiss Medicine:

An HIV-infected person with potent [antiretroviral therapy, defined as "combination therapy against HIV which reduces the viral load below the limit of detection"] is not sexually infectious, i.e. does not transmit [HIV] via sexual contacts as long as the therapy is practiced consistently and monitored regularly by the treating physician; the viral load on [antiretroviral therapy] has been below the limit of detection for at least six months; [and] no infections with other STIs are present. Under these circumstances, potent [antiretroviral therapy] therefore definitely prevents HIV transmission as safely as condoms.

Vernazza and his wife went on vacation. The phone began to ring and didn't stop. Vernazza was, he said, "completely overwhelmed" by the response.

Almost all of it was negative.

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This article was provided by TheBody.

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