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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

A number of follow-up studies since have also reported significant reductions in HIV transmission and numbers of new infections averted. 3 4 5

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 Zidovudine (AZT) has been used to prevent HIV transmission from mother to child and had also been used as post exposure prophylaxis (PEP) 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

One study from the UK and Ireland found that pregnant women who received at least 14 days of ART reduced the risk of transmitting HIV to their babies to less than 1 percent. 10

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 Taking antiretroviral treatmentIn 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

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