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HIV Treatment as Prevention
Treatment as prevention (TASP) is a term increasingly used to describe HIV prevention methods that use antiretroviral treatment to decrease the chance of HIV transmission.
People living with HIV often take treatment for their own health; ARVs decrease the amount of the virus in a person’s bodily fluids, known as the ‘viral load’, thereby reducing the likelihood of AIDS-related illnesses. 1 An HIV-positive person’s viral load is the single biggest risk factor in the transmission of HIV. 2 Therefore, taking treatment has the additional benefit of significantly decreasing this risk. The idea of ‘treatment as prevention’ is to use treatment as a prevention strategy that individuals could use to protect their sexual partners, or, on a large scale, to reduce HIV transmission among a population.
When is it appropriate to use HIV treatment as prevention?
An individual may choose to initiate treatment earlier, if given this option, to help prevent the transmission of HIV to sexual partner(s). This can be appropriate if they are given sufficient counselling and guidance for their specific situation, and TASP is seen as one of various prevention options. 3
On a public health level, the use of treatment as prevention is still widely debated. 4 Initiatives should consider the rights of the individual. Antiretroviral treatment can cause serious side effects and can lead to drug resistance if not taken exactly as prescribed. Therefore an HIV-positive person has the right to decide whether or not to take the treatment by weighing up the potential disadvantages and benefits for their own health.
How is HIV treatment currently being used to prevent HIV infections?
Antiretroviral therapy is already used in several ways to prevent HIV from being transmitted. These uses are often cited in arguments that support the idea of treatment as prevention being utilised on a larger scale, to lower transmission rates among a population. 5 6
- Prevention of mother-to-child transmission (PMTCT): Across the world, HIV-positive pregnant women take antiretroviral drugs to reduce the chances of transmitting HIV to their baby. Without intervention there is a 20-45 percent chance that a baby born to an HIV-infected mother will become infected. 7 However, treatment for the mother during pregnancy significantly reduces this risk.
- Post exposure prophylaxis (PEP): In some countries if a person has been exposed to HIV they are offered a short course of antiretroviral drugs to reduce their chances of becoming infected with the virus. This is called post exposure prophylaxis, or PEP, and is used in both occupational and non-occupational settings. Health care workers are offered the treatment if they have received a needlestick injury or have been exposed to HIV through their work. A combination of studies have suggested that it may be effective in reducing the risk of HIV infection. 8 9 10
- Pre-exposure prophylaxis (PrEP): One possible prevention technique that is being researched is pre-exposure prophylaxis. 11 PrEP involves providing people who are not infected with HIV with antiretroviral drugs before possible exposure to the virus, to stop them from becoming infected. It has the potential to be useful for serodiscordant couples (couples where only one partner is living with HIV).
Countries are starting to implement treatment as prevention with various approaches. The United States recommends treatment for all people living with HIV regardless of CD4 count. Countries such as France, Uruguay and Algeria recommend or consider treatment for HIV-positive people without symptoms, with CD4 counts between 350 cells/mm3 and 500 cells/mm3. Many countries worldwide, such as Zambia, now implement TASP for serodiscordant couples. 12
What about the idea of HIV treatment as prevention for tackling the global AIDS epidemic?
Treatment as prevention could have various impacts on public health. On a community level, it has been seen that as the number of people taking more effective HIV treatment has risen, community viral load has decreased, resulting in a reduction of new HIV infections. 13 14 San Francisco was the first health authority in the world to offer treatment to all people diagnosed with HIV, regardless of cell count. 15 The increased access meant that the average viral load among people living with HIV fell by 40 percent between 2004 and 2008, and this coincided with new infections dropping by a third. 16 In Lesotho, there has been a recent decline in new infections, even though risk-taking behaviour has increased among some populations, suggesting that the drop is due to more people accessing treatment. 17
“an HIV positive person who is taking effective antiretroviral therapy, who has an undetectable viral load and is free from STDs, has a negligible risk of infecting others with the virus. ”
In 2008 a group of Swiss scientists produced the first ever consensus statement that asserted that an HIV positive person who is taking effective antiretroviral therapy, who has an undetectable viral load and is free from STDs, has a negligible risk of infecting others with the virus. 18 Their conclusion was drawn from the results of studies that showed that if an effective treatment regimen were followed, a person living with HIV will not pass on the virus to their HIV-negative partner. (For more information on this issue read AVERT's HIV transmission and antiretroviral therapy briefing sheet).
Since the Swiss statement, various studies have emerged that have investigated the relationship between viral load and HIV transmission. For example:
- A large, randomised, placebo-controlled trial involving 3381 heterosexual African couples found antiretroviral therapy use by the HIV infected partner was associated with a 92 percent reduction in risk of HIV-1 transmission to their fellow partner. 19
- In 2011, the HPTN 052 study involving 1,763 HIV serodiscordant couples was completed. 20 21 Interim analysis of the results showed those who started antiretroviral therapy as soon as they were diagnosed significantly lowered the risk of HIV transmission to their sexual partners, compared to those starting treatment later, when their CD4 count had fallen below 250 cells/mm3. Of those who took part in the study and were infected from their partner, one person became infected from the early ARV group, versus 27 from the later ARV group, showing a 96 percent reduction in risk of transmission. 22
- The first study in a general population setting showed that in areas where there is higher (greater than 30 percent of the HIV positive population) uptake of antiretroviral therapy, people who do not have HIV are 38 percent less likely to acquire the virus than in areas of low uptake (less than 10 percent). 23 24
Taking into account the effect that access to ARVs has on a population’s transmission rate, the ‘Swiss statement’ and these other studies, some advocates have argued that a way to reduce the global AIDS epidemic would be to test everyone in 'high risk' groups and areas of generalised epidemics, and then immediately treat all of those diagnosed positive, regardless of whether their immune system is damaged. 25 Various trials of the ‘test and treat’ strategy at a community level are currently being developed and implemented. 26 One trial is being tested on a large scale trial in KwaZulu-Natal, one of South Africa's provinces most affected by HIV and AIDS. The Treatment as Prevention (TasP) trial was launched in July 2011 and is hoped to last until 2015. 27 28
“researchers now enter a new era with a critical question to be answered: is the preventive effect of ART highly beneficial at the population level? Should this concept be proven, it would have major implications for the public health approach of prevention and treatment ” Professor Jean-François Delfraissy, Director of ANRS, organisation supporting the study
In 2011, a group of more than twenty HIV organisations from around the world, as well as hundreds of individuals, signed a declaration calling for country governments, multilateral organisations, and civil society to begin to use the evidence from the HPTN 052 trial to actively work towards early access to HIV treatment. 29 The declaration also called for countries and donor programs to collect and monitor data in order to assess the feasibility and cost-effectiveness of increasing the treatment initiation threshold for people living with HIV from 350 cells/mm3, (the current WHO recommendation) to 500 cells/mm3.
“Now is the time to change the approach to the epidemic.”
- ‘We CAN End the AIDS Epidemic’ Declaration 30
It has been observed that although on a national scale behaviour change programmes bring down infection rates in the first stages of an epidemic, the numbers of new HIV infections tend to stabilize. UNAIDS suggest that treatment as prevention could help to change this pattern and allow new infection rates to continue to decrease. 31
Would the 'test and treat' strategy work?
Granich et al have developed a mathematical model to calculate the possibility of the HIV epidemic being driven towards elimination through a ‘test and treat’ strategy. 32 They estimate that if this strategy was implemented in South Africa, where there is a generalised epidemic, after 2032 the cost of the epidemic would be less than under the current strategy.
However, whether the model would actually work within a community or population is debated. 33 34 Canada, the US and Europe have been cited as places where HIV transmissions have not been reduced through the roll-out of ARVs. 35 One study which looked at infections among serodiscordant couples in China did not find an association between HIV transmission and viral load, instead identifying duration of follow-up after being treated as the main factor affecting HIV transmission. The study concluded that prevention interventions for discordant couples should focus on support and education services and helping people to adhere to treatment. 36
When a person becomes infected with HIV it can take up to three months before the virus is detected by standard antibody tests. If a person is tested during this time they may receive a ‘false negative’ result, which means that even though the test is negative, they are in fact infected with HIV. It is also during this period of time when they are most infectious. Research suggests that up to two thirds of HIV transmission occurs during this period of ‘acute HIV infection’. 37
Therefore even if everyone who tested positive for HIV were treated with antiretroviral therapy, there would still be a group of people who had received a false negative result and who could still transmit the virus to others. For ‘test and treat’ to work among those people who did test positive, all those on treatment would need to adhere to it, which may be unlikely. Additionally, it is possible for viral load to change even when treatment is adhered to. 38
What would be the effects on the individual?
The HPTN 052 study found benefits for the individual beyond the preventative benefit. Although early probability of death did not decrease significantly, early antiretroviral therapy was found to decrease chance of HIV-related clinical events by 41 percent. 39
However, once a person starts taking antiretroviral treatment, they have to take it exactly as prescribed, and for the rest of their life. If not, they significantly increase the risk of drug resistance. In addition, antiretroviral drugs often have unpleasant side effects and there are possible long-term effects of treatment, such as diabetes, body fat changes and potentially others that remain unknown. 40 These are some of the reasons why in most settings treatment is currently only recommended when HIV has attacked the immune system to an extent where, without treatment, the person's health will start to deteriorate. 41 For many people living with HIV this means not starting treatment for years. Starting treatment at an earlier stage could therefore potentially be detrimental to the individual's health.
The ‘test and treat’ strategy could be viewed as unethical on the basis that medical codes of practice should make the care of the individual patient the doctor's first concern. Individuals may refuse to take treatment if they didn’t need to for their own health, and forcing them to against their will could be seen as an abuse of human rights. This issue has already emerged in the example of San Francisco, where gay men are encouraged to be tested for HIV every six months. Those with a positive diagnosis are recommended to start treatment immediately, under the health authority’s strategy to reduce new infections by 91 percent over ten years. 42 However, it has been claimed that individuals are recommended early treatment for their own health, without clarity around how TASP is a strategy for the wider population / public health. In the UK, clinicians are advised to discuss the potential of HIV treatment to protect sexual partners, emphasising the choice of the person living with HIV. People living with HIV need to be informed truthfully about all factors relevant to beginning treatment. 43
Another potential issue is that if people become too confident in the preventative effects of treatment, they may be more likely to engage in high-risk behaviour. A study of MSM in Boston who were taking highly active antiretroviral therapy (HAART) found that 18 percent had HIV in their blood, and 50 percent had HIV in their semen. 44 The presence of the virus was strongly associated with the presence of genital infections and inflammation, as well as the individual having engaged in unprotected sex, showing that the chance of transmission for a person using treatment as prevention is still influenced by other factors.
There are also various concerns around the availability of TASP for individuals, for example those in serodiscordant relationships. These include the possibility of people living with HIV experiencing external pressure or compulsion to take treatment, either from partners or, as TASP becomes more widespread, from general society. 45
Is it feasible?
HIV testing: Stigma, criminalisation and human rights abuses act as strong deterrents to accessing testing services, making it impossible to detect all HIV infections even in well-resourced countries. In the United States of America, for example, around one in five people living with HIV are unaware of their infection, 46 and many people are still only tested once they have been diagnosed with an opportunistic infection. It has been calculated that, for treatment as prevention to work on a public health level, at least 75 percent of HIV positive people must be diagnosed and treated. 47 Barriers that prevent people from getting tested would therefore need to be addressed.
HIV treatment: Many countries have rapidly increased the number of people accessing treatment in recent years. Today, 65 percent of people in need are receiving treatment and twelve low- and middle-income countries have reached universal access. 48 In many countries, however, access to treatment continues to be limited, and where treatment is available, many peole with HIV are not eligible to start antiretroviral treatment until their CD4 counts are already low. Cosequently, if treatment targets cannot be reached now, it is highly unlikely there would be enough funding to treat those whose HIV infection has not yet significantly damaged their immune system.
HIV care: Care is needed to ensure people living with HIV receive and adhere to effective antiretroviral therapy, to keep viral load to a minimum. In one review of access to HIV services in the USA, poor engagement in care was cited as a significant challenge to the idea of a 'test and treat' strategy for HIV prevention. 49 There would need to be a large increase in healthcare workers as treatment was expanded. Concerns have been raised around the feasibility of training the influx of staff in important issues such as the impact of stigma and avoiding the coercion of patients. 50
Other costs: The 'test and treat' mathematical model proposed by Granich and colleagues 51 has been criticised for substantially underestimating the actual costs that it would entail. 52 In addition to the cost of providing more antiretroviral drugs, there would be administrative and human resources obstacles. These include finding additional doctors and nurses to prescribe the drugs, extra counsellors for pre and post-test counselling, and staff to support and encourage adherence among those taking treatment. It would be extremely difficult for countries to find the money for these costs in addition to finding the money to provide universal treatment. However, it has been argued that although in the short term the 'test and treat' strategy would be very costly, it has the potential to be cost-effective in the long term. 53
Is there a future for treatment as prevention?
Using HIV treatment as prevention to tackle the global AIDS epidemic does have some advantages; it would significantly increase the number of people who are aware of their HIV status, and millions of people worldwide who are in immediate need of HIV treatment would receive it. However, for treatment as prevention to work on this level, each case needs to be assessed on its own merit. The rights of the individual to choose whether to be treated before they actually need treatment for their own health, would have to be paramount.
HIV treatment is already being used as a prevention method in the cases of PMTCT and PEP, and populations are already benefiting from the lowered rates of new infections that accompany more people taking antiretroviral therapy.
If an individual wishes to use treatment as their prevention method they need to be aware that risk is reduced not eliminated, and be fully supported with decisions around safer sex, condom use and viral load.
If treatment as prevention were utilised on a public health level, it would still need to be ensured that people living with HIV have access to appropriate advice on how different prevention techniques can be used to manage risk, in monogamous and non-monogamous relationships. 54 Treatment as prevention would need to be complemented by education, condom use and behaviour change - other prevention strategies that have in many cases been largely successful. 55 As the Joint United Nations Programme on HIV/AIDS state:
"UNAIDS strongly recommend a comprehensive approach to HIV prevention that plans and delivers an evidence informed and human rights based combination of programmes and policies, tailored to meet the needs of those most at risk, and including practical programmes to reduce underlying causes of vulnerability, such as gender inequality and HIV related stigma and discrimination... Antiretroviral therapy will play several roles in combination prevention strategies, along with other key strategies." 56
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- 13. Das-Douglas, M et al (2010) 'Decreases in community viral load are associated with a reduction in new HIV diagnoses in San Francisco', Session 10-Oral Abstacts, Paper #33, 17th Conference on Retroviruses and Opportunistic Infections
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- 23. Tanser F. et al (2012) ‘ Effect of ART Coverage on Rate of New HIV Infections in a Hyper-endemic, Rural Population: South Africa’ 19th Conference on Retroviruses and Opportunistic Infections
- 24. UNAIDS (2012) ' UNAIDS welcomes further evidence of the positive impact of antiretroviral therapy on preventing new HIV infections'
- 25. Granich, R.M et al (2009) 'Universal voluntary HIV testing with immediate antiretroviral therapy as a strategy for elimination of HIV transmission: a mathematical model', The Lancet, 2009; 373: 48-57.
- 26. Williams B. et al (2010) ‘ Treatment as prevention: preparing the way’ Journal of the International AIDS Society, 14 (1)
- 27. Africa Centre, ANRS & University of KwaZulu-Natal (2010, 29th November) Press release: 'What would be the impact of universal Test and Treat on the HIV pandemic?' [PDF]
- 28. ANRS (2011) ' Le rapport du séminaire inaugural sur "le traitement comme prévention (TasP)” a été rendu public le 19 juillet 2011'
- 29. AVAC (2011, June 7th) ' We CAN End the AIDS Epidemic'
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- 31. UNAIDS (2011) ' UNAIDS World AIDS Day Report 2011'
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- 33. Cohen M. (2010) ‘ HIV Treatment as Prevention: To be or not to be?’ Journal of Acquired Immune Deficiency Syndrome, 55 (2)
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- 41. WHO (2009, 30th November) 'Rapid advice: antiretroviral therapy for HIV infection in adults and adolescents'
- 42. NAT (2011, May) ' HIV Treatment as Prevention'
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- 44. Medical News Today (2012, 29th March) ' HIV-Infected Men At Risk For Spreading HIV Despite Taking HAART'
- 45. aidsmap / nam (2012, June 15th) ' If people who need HIV drugs aren’t getting them now, why should the prevention benefit of treatment be the reason that the drugs become available?'
- 46. CDC (2010, July) 'HIV in the United States'
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- 48. WHO (2013, June) ' Global update on HIV treatment 2013: Results, Impact and Opportunities'
- 49. Gardner, E.M et al (2011) 'The spectrum of engagement in HIV care and its relevance to test-and-treat strategies for prevention of HIV infection', Clinical Infectious Diseases, 2011;52(6)793-800
- 50. aidsmap / nam (2012, June 15th) ' If people who need HIV drugs aren’t getting them now, why should the prevention benefit of treatment be the reason that the drugs become available?'
- 51. Granich, R.M et al (2009) 'Universal voluntary HIV testing with immediate antiretroviral therapy as a strategy for elimination of HIV transmission: a mathematical model', The Lancet, 2009; 373: 48-57.
- 52. Wagner, B & Blower, S (2010, 18th September) 'Cost of eliminating HIV in South Africa have been underestimated', The Lancet, 376:953
- 53. Johnston, K.M et al (2010) 'Expanding access to HAART: a cost-effective approach for treating and preventing HIV', AIDS 2010, Jul 31;24(12):1929-35
- 54. NAT (2011, May) ' HIV Treatment as Prevention'
- 55. Venkatesh, KA. et al (2011, October) ' Is expanded HIV treatment preventing new infections? Impact of antiretroviral therapy on sexual risk behaviors in the developing world' AIDS 25(16)
- 56. UNAIDS (2009, 6th November) 'Antiretroviral treatment for prevention'