Good morning, and thank you for asking us to appear before the committee today.
My name is Sean Hosein, and I am the Science and Medicine Editor at CATIE. For more than 30 years, I have reviewed research on HIV prevention and treatment and disseminated this news in plain language to people living with HIV, their health care providers and the broad range of service providers working in Canada's HIV/AIDS response.
One of the most exciting developments in HIV research that I have witnessed in my career has been the evolution of our knowledge on the impact of HIV viral load on the possibility of transmission. Between 2011 and 2018, four large clinical trials have now confirmed that people living with HIV who have a suppressed viral load do not transmit the virus to their sexual partners.
When people living with HIV take their medication as prescribed, it can reduce the amount of virus in their body to levels so low that they cannot be detected by standard blood tests. We call this “undetectable viral load” or “viral suppression”. According to the latest estimates from the Public Health Agency of Canada, 91% of HIV-positive Canadians on treatment have achieved viral suppression, and this proportion could be higher with greater access to treatment and care. In the United Kingdom, the equivalent proportion is 97%.
In the four large clinical trials I previously mentioned, out of more than 100,000 instances of sex without a condom with an HIV-positive partner, there were zero confirmed cases of HIV transmission when the HIV-positive partner had a suppressed viral load. For the purpose of these studies, this meant that they had less than 200 copies of HIV per millilitre of blood.
As published in an editorial in the eminent medical journal The Lancet in 2017, the evidence to support the effectiveness of viral suppression in blocking transmission is clear. Where the evidence is less clear is in the likelihood of transmission in the absence of viral suppression. Quantifying this is difficult due to the challenges of conducting a robust study that tracks the number of potential HIV exposures within a couple over time, what type of sex they had, whether they used prevention tools and any biological factors.
Despite these challenges, attempts have been made to calculate the average HIV transmission possibility. There is no possibility of an HIV-negative person contracting HIV when receiving oral sex from an HIV-positive person with or without a viral suppression. There is a theoretical possibility of HIV transmission from performing oral sex on an HIV-positive man when ejaculate is present, although there is limited evidence to confirm this. If such transmission were possible, it would be a negligible risk, at most.
When a condom is used consistently and correctly, HIV transmission is not possible with or without viral suppression. Laboratory tests have confirmed that condoms are impermeable to HIV, including condoms made of latex, polyurethane, nitrile or polyisoprene. These estimates are synthesized in the expert consensus statement on the science of HIV in the context of criminal law published in 2018 by 20 of the world's leading scientists.