This symposium provided a great analysis of some of the issues confronting prevention efforts. Julie Overbaugh gave a great overview of HIV biology, particularly that period of time known variously as HIV stage 0, pre-seroconversion and/or early infection. She emphasised that this was the period before viral-load peaks and a time where it is very difficult to study what is happening in humans as they are not aware they are infected. Macaques provide the study model, but given the complexity of this period even slight differences between the hosts and the viruses might introduce great variation. So with that caveat she explained that there is considerable dissemination of virus int he first 1 - 3 days and by days 3 - 7 the reservoir is establishing in gut and lymph nodes. The impact of prevention diminishes as the reservoir is established.
She also suggested that there is selective pressure not just from the dominant virus but that CCR5 is more common in transmission that CXCR4 virus, making R5 inhibitors logical for PrEP. CCR5 virus is also more resistant to interferon, which is produced in a storm during infection. She lastly she compared cell to cell infection and cell free virus, and suggested that infection may be facilitated to hindered depending on whether cell to cell or cell free viruses are the target. Meaning that what drives transmission in breast feeding for example may be very different from what is important in vaginal transmission.
Christophe Fraser discussed phylogenetics and gave a detailed analysis of comprehensive sequencing of virus in the Netherlands. He suggested that about 69% of new infections were originating from the undiagnosed and ~24% from diagnosed but not on treatment and only 7% from people on ART. Immediate treatment could be expected to result in a reduction of between 25-30% of transmissions. PrEP and treatment might result in a reduction of 50-60% of infections, summarising that there is a lot to do to push prevention beyond where we are now.
Richard Elion building on the this reviewed optimising ART and looked at Treatment as Prevention. He made the statement that "we can't just treat our way out." He suggested that we need to better know where infections are occurring in populations and compared the treatment cascade between a number of countries. But to illustrate this point he then dissected the 19% of people with HIV in the USA who are estimated to have suppressed virus a number of ways: 6% of people under 30 and 28% over thirty; 16% black MSM and 34% Caucasian. He also questioned some of the definitions within the cascade. and challenged what was meant by "in care" when 74% are in continuous care while 26% are in only sporadic care. He ended his talk by looking at how to engage the unengaged and identified: stigma, delivery methods, integration of bio-medical approaches and resourcing as the critical issues. This led seamlessly into the last talk.
Jeffrey Crowley looked at HIV criminalisation and suggested that laws are not protective, even though law makers might want them to be. And in places with a high prevalence it is unrealistic to expect the assumption of negativity. He pointed out the important role of health care workers in educating about HIV and pointed out that provisions such as anti-discrimination legislation are not sufficient alone to remove stigma.
Australia was referred to in the questions. A country which has excelled in the response but which is still seeing sustained incidence. The strong take-home message from this session was the importance of biomedical prevention to interrupt the the establishment of infection. This will challenge many attitudes but it may, in combination with treatment and testing, be the only way to significantly reduce new infections, particularly in settings, such as ours, where retention in care, treatment and viral suppression are approaching their maximum potential.
The session was symposium S-5 4.00 pm - 6.00 pm Wednesday Advancing HIV prevention. You can view it from the webcast http://www.croiwebcasts.org/