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HIV Treatment as Prevention
Treatment as prevention (TasP) refers to HIV prevention methods that use antiretroviral treatment (ART) to decrease the risk of HIV transmission. ART reduces the HIV viral load in the blood, semen, vaginal fluid and rectal fluid to very low levels ('undetectable'), reducing an individual's risk of HIV transmission. 1
For a number of years now, there has been growing evidence of the benefits of HIV treatment as a prevention method. In 2011, a landmark study, HPTN 052, showed early initiation of antiretroviral treatment (in people with a CD4 count between 350 and 550) for the HIV-positive partner in a serodifferent couple reduced HIV transmission to the HIV-negative partner by 96 percent. 2
This has led to the idea that treatment as prevention could be utilised as part of a "test and treat" strategy by increasing testing and treatment coverage as well as decreasing community viral load. 6
Following the results of HPTN 052, Michel Sidibé, the Executive Director of UNAIDS, commented:
“This breakthrough is a serious game changer and will drive the prevention revolution forward. It makes HIV treatment a new priority prevention option" 7
HIV treatment is already being used as prevention
Prevention of Mother-to-Child Transmission (PMTCT)
Treatment as prevention has been utilised since the mid-1990s to prevent the mother-to-child transmission (MTCT) of HIV. In 1994, research showed zidovudine (AZT) given to HIV-infected mothers and their babies reduced MTCT from 25 percent to 8 percent. 8
Since then, testing pregnant women and treating HIV-positive mothers with antiretroviral drugs (ARVs) during pregnancy, delivery and breastfeeding has been found to reduce the risk of a mother transmitting HIV to her child by up to 90 percent. 9
Pre-exposure prophylaxis (PrEP)
Pre-exposure prophylaxis (PrEP) is an HIV prevention strategy that uses ARVs to protect HIV-negative people from HIV. By taking ARVs before HIV exposure, a person's risk of HIV infection is lowered. When taken consistently, PrEP has been shown to reduce the risk of HIV transmission by up to 92 percent. As a result, like TasP, it potentially has population-wide benefits. 11
However, if not taken routinely and consistently, PrEP is much less effective. One study has suggested using PrEP in combination with TasP, depending on local circumstances. Specifically, it says PrEP could be used where HIV prevalence is roughly 5 percent and TasP reduces transmission by over 50 percent. 12
Moreover, it should also be targeted at groups with high rates of HIV transmission including sex workers, young women, men who have sex with men (MSM) and people who inject drugs. 13 However, PrEP is not yet widely available.
Post-exposure prophylaxis (PEP)
Post-exposure prophylaxis (PEP) is short-term antiretroviral treatment taken after possible exposure to HIV. Since 1998, it has been used for healthcare workers who may have been exposed to HIV-infected fluids. 14 More recently, it has been used to treat those who may have been exposed during a single event (e.g. sexual assault, unprotected sex or sharing drug injecting equipment). 15
More research is needed on the effectiveness of PEP as an HIV prevention strategy. One trial from the mid-1990s, which gave AZT to healthcare workers exposed to HIV, prevented transmission in 81 percent of cases. 16 However, the use of AZT in PEP has since been replaced by tenofovir as a component of a three-drug combination. 17
Test and treat strategies
"Test and treat" programmes are based on the premise that the rate of new HIV infections can be reduced by rolling out universal HIV testing in order to diagnose all people living with HIV, initiate antiretroviral treatment regardless of CD4 count or viral load.
One study from South Africa estimated that the implementation of universal voluntary HIV testing in South Africa for adults over 15 years old would decrease HIV prevalence to 1 percent within 50 years. 18
Trials testing the effectiveness of TasP for the general population in communities in sub-Saharan Africa with high HIV prevalence are currently ongoing. They aim to compare the effects of TasP on HIV transmission by offering ART to people with a CD4 count under 350. 19 20
Limitations of treatment as prevention
TasP is not 100% effective
Following the results of the HPTN 052 study, in 2013 the World Health Organisation (WHO) recommended that antiretroviral treatment be offered to all people living with HIV who have uninfected partners ( serodifferent couples) to reduce HIV transmission. 21
However, even if all serodifferent couples had access to TasP, it is widely agreed this would not bring an end the epidemic. If the preventative benefits of treatment are overstated, people are more likely to engage in high-risk behaviours. For example, research from Switzerland showed how increased access to antiretroviral treatment can lead to a reduction in other HIV prevention measures such as condom use. 22
Indeed, a number of studies have reported much lower reductions in HIV transmission raising doubts about TasP as a public health intervention. Research from China of 38,000 serodifferent couples reported that treating the HIV-infected partners reduced the risk of HIV transmission to the uninfected partner by a comparatively low 26 percent. 23 Moreover, in the HPTN 052 study, 30 percent of HIV-positive people had an external partner. 24
TasP, adherence and multiple drug resistance
The success of TasP is highly dependant upon people adhering to antiretroviral treatment (ART). It is widely agreed that once ART is initiated it should not be interrupted, as incomplete viral suppression causes the more sensitive strains of HIV to be suppressed and the resistant strains to become dominant. Resistant strains are harder to treat. 25
Adherence is an issue even where ART is widely available. In 2011, one study from the United States reported that 15 years after the initiation of highly active antiretroviral therapy (HAART), and 4 years after the introduction of combination prevention, only 19 percent of 1.1 million people living with HIV in the country had an undetectable viral load. 26 In South Africa, which has the largest ART programme in the world, one study found that only 64 percent of people who were initiated on treatment between 2002 and 2007 were still in care 3 years on. 27
Concerns have also been that the widespread use of antiretroviral treatment at a population level to reduce the number of new HIV infections would lead to a significant increase in multiple drug resistant HIV (MDR) levels. Indeed, the dramatic scaling up of ART could see increases in non-adherence resulting in the development of resistant strains of the virus. 28 One study from LA County, USA, reported that the use of 'test and treat' among MSM could almost double the prevalence of MDR HIV cases from 4.8 percent to 9.1 percent by 2023 among this group. 29
Despite legitimate arguments about ART adherence and drug resistance, many argue that TasP interventions should be implemented regardless given the prevention benefits and how existing combination treatment has proved effective in suppressing viral load. Moreover, there remains a lot of scope to improve the current delivery of treatment through improved monitoring of ART adherence as well as strengthening the links between treatment and care. 30
The future of treatment as prevention
Treatment as prevention (TasP) has a lot of potential in reducing population level rates of HIV transmission by increasing uptake of HIV testing, offering ART and linking people to care. 31
However, the effectiveness of TasP relies, at least in part, on the willingness and ability of people on treatment to remain in care and follow their prescribed course of antiretroviral drugs, adhering to them correctly. A number of studies have promoted a combination of cognitive, behavioural and mixed interventions including emotional support as means of improving adherence to ART. 32 33 34
Others have suggested that more research is needed in order to identify the most effective way of delivering TasP. Research from Botswana has modelled the benefits of targeting such a strategy at people with the lowest CD4 counts. 35
Bigger challenges and questions remain around the implementation of TasP in resource-limited settings. Indeed, its success depends much upon the ability of a country's healthcare service to deliver these services. 36 37 However, with TasP trials on-going, the burden of adding treatment-based prevention to already strained healthcare systems remains unknown. 38
Ethical and public health concerns have also been raised about how limited supplies of antiretroviral drugs in resource-poor countries are distributed - for treatment, prevention or both. One study concludes it is "unethical to watch patients with treatable AIDS worsen and die, even with supportive care, so that medications for treatment can be diverted for prevention." 39 However, others maintain that while TasP requires large financial investments and poses significant implementation challenges, it is potentially a highly cost-effective approach to reducing both new HIV infections and the overall global HIV burden. 40
Overall, there is a wide consensus supporting treatment as an HIV prevention measure, especially in those with CD4 counts under 350. Treatment for this group must be scaled up, with healthcare systems working to increase adherence and retention in care. However, it is widely acknowledged that treatment alone will not end the global HIV epidemic. In order to be effective, TasP needs to be delivered as part of a comprehensive package of prevention methods including HIV and AIDS education, sexual and reproductive health education, condom use and behaviour change. 41
- 1. WHO (2012) ' Antiretroviral treatment as prevention (TASP) of HIV and TB'
- 2. Cohen, M.S. et al (2011) ' Prevention of HIV-1 Infection with Early Antiretroviral Therapy' The New England Journal of Medicine 365(5):493-505
- 3. Baeten, J.M. et al (2012) ' Antiretroviral Prophylaxis for HIV Prevention in Heterosexual Men and Women' The New England Journal of Medicine 367(5):399-410
- 4. Thigpen, M.C. et al (2012) ' Antiretroviral Preexposure Prophylaxis for Heterosexual HIV Transmission in Botswana' The New England Journal of Medicine 367:423-434
- 5. Das, M. et al (2010) ' Decreases in Community Viral Load Are Accompanied by Reductions in New HIV Infections in San Francisco' PLOS One 5(6):e11068
- 6. CATIE (2013) ' Treatment as prevention: do the individual prevention benefits translate to the population level?'
- 7. UNAIDS (2011, 12 May) ' Groundbreaking trial results confirm HIV treatment prevents transmission of HIV'
- 8. Connor, E.M. et al (1994) ' Reduction of Maternal-Infant Transmission of Human Immunodeficiency Virus Type 1 with Zidovudine Treatment' The New England Journal of Medicine 331:1173-1180
- 9. CDC (2006) ' Achievements in Public Health: Reduction in Perinatal Transmission of HIV Infection --- United States, 1985--2005' MMWR 55(21):582-597
- 10. Townsend, C.L. et al (2008) ' Low rates of mother-to-child transmission of HIV following effective pregnancy interventions in the United Kingdom and Ireland, 2000-2006' AIDS 22(8):973-981
- 11. Naswa, S. and Marfatia, Y.S. (2011) ' Pre-exposure prophylaxis of HIV' Indian Journal of Sexually Transmitted Diseases 32(1):1-8
- 12. Williams, B.G. et al (2012) ' Pre-exposure prophylaxis (PrEP) versus treatment-as-prevention (TasP) for the control of HIV: Where does the balance lie?' Cornell University Library
- 13. Williams, B.G. et al (2012) ' Pre-exposure prophylaxis (PrEP) versus treatment-as-prevention (TasP) for the control of HIV: Where does the balance lie?' Cornell University Library
- 14. Henderson, D.K. and Gerberding, J.L. (1989) ' Prophylactic zidovudine after occupational exposure to the human immunodeficiency virus: an interim analysis' The Journal of Infectious Diseases 160(2):321-327
- 15. Smith, D.K. et al (2005) ' Antiretroviral Postexposure Prophylaxis After Sexual, Injection-Drug Use, or Other Nonoccupational Exposure to HIV in the United States' MMWR 54(2):1-20
- 16. Cardo, D.M. et al (1997) ' A Case–Control Study of HIV Seroconversion in Health Care Workers after Percutaneous Exposure' The New England Journal of Medicine 337:1485-1490
- 17. BHIVA (2014, 10 September) ' Change to the recommended regimen for post-exposure prophylaxis (PEP)'
- 18. Granich, M.D. et al (2009) ' Universal voluntary HIV testing with immediate antiretroviral therapy as a strategy for elimination of HIV transmission: a mathematical model' The Lancet 373(9657):48-57
- 19. Cori, A. et al (2014) ' HPTN 071 (PopART): A Cluster-Randomized Trial of the Population Impact of an HIV Combination Prevention Intervention Including Universal Testing and Treatment: Mathematical Model' PLOS One 9(1):e84511
- 20. Iwuji, C.C. et al (2013) ' Evaluation of the impact of immediate versus WHO recommendations-guided antiretroviral therapy initiation on HIV incidence: the ANRS 12249 TasP (Treatment as Prevention) trial in Hlabisa sub-district, KwaZulu-Natal, South Africa: study protocol for a cluster randomised controlled trial' Trials 14:230
- 21. WHO (2013) ' Consolidated guidelines on the use of antiretroviral drugs for treating and preventing HIV infection'
- 22. Hasse, B. et al (2010) ' Frequency and determinants of unprotected sex among HIV-infected persons: the Swiss HIV cohort study' Clinical Infectious Diseases 51(11):1314-1322
- 23. Jia, Z. et al (2013) ' Antiretroviral therapy to prevent HIV transmission in serodiscordant couples in China (2003-11): a national observational cohort study' Lancet 382(9899):1195-1203
- 24. Cohen, M.S. et al (2011) ' Prevention of HIV-1 Infection with Early Antiretroviral Therapy' The New England Journal of Medicine 365(5):493-505
- 25. AIDSinfo (2014) ' Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents'
- 26. 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 52(6):793-800
- 27. Cornell, M. et al (2010) ' Temporal changes in programme outcomes among adult patients initiating antiretroviral therapy across South Africa, 2002-2007' AIDS 24(14):2263-2270
- 28. Shelton, J.D. (2011) ' ARVs as HIV Prevention: A Tough Road to Wide Impact' Science 334:1645-1646
- 29. ScienceDaily (2013, 18 March) ' Widespread 'test-and-treat' HIV policies could increase dangerous drug resistance'
- 30. Gupta, R.K. et al (2013) ' Oral Antiretroviral Drugs as Public Health Tools for HIV Prevention: Global Implications for Adherence, Drug Resistance, and the Success of HIV Treatment Programs' The Journal of Infectious Diseases 207(Supplement 2):101-106
- 31. Smith, L. et al (2011) ' HIV-1 treatment as prevention: the good, the bad, and the challenges' Current Opinion in HIV and AIDS 6(4):315-325
- 32. Dewing, S. et al (2014) ' Antiretroviral adherence interventions in Southern Africa: implications for using HIV treatments for prevention' Current HIV/AIDS Reports 11(1):63-71
- 33. Scheurer, D. et al (2012) ' Association between different types of social support and medication adherence' The American Journal of Managed Care 18(12):461-467
- 34. Jones, D.L. et al (2007) ' Efficacy of a Group Medication Adherence Intervention Among HIV Positive Women: The SMART/EST Women’s Project' AIDS and Behaviour 11(1):79-86
- 35. Novitsky, V. et al (2010) ' HIV-1 Subtype C-Infected Individuals Maintaining High Viral Load as Potential Targets for the “Test-and-Treat” Approach to Reduce HIV Transmission' PLOS One 5(4):e10148
- 36. Sigaloff, K.C.E. et al (2014) ' Global Response to HIV: Treatment as Prevention, or Treatment for Treatment?' Clinical Infectious Diseases 59(Supplement 1):7-11
- 37. Harries, A.D. et al (2010) ' The HIV-associated tuberculosis epidemic—when will we act?' The Lancet 375(9729):1906-1919
- 38. Padian, N.S. et al (2011) ' HIV prevention transformed: the new prevention research agenda' Lancet 378(9787):269-278
- 39. Macklin, R. et al (2012) ' Given Resource Constraints, It Would Be Unethical To Divert Antiretroviral Drugs From Treatment To Prevention' Health Affairs (Project Hope) 31(7):1537-1544
- 40. Wilson, D. et al (2014) ' The economics, financing and implementation of HIV treatment as prevention: What will it take to get there?' African Journal of AIDS Research 13(2):109-119
- 41. Venkatesh, K.A. et al (2011) ' Is expanded HIV treatment preventing new infections? Impact of antiretroviral therapy on sexual risk behaviors in the developing world' AIDS 25(16)
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