Tuesday, September 2, 2014

Antiretroviral treatment prevents AIDS

Antiretroviral treatment (ART) manages an HIV infection by hampering the ability of the virus to attack the immune system's T-helper cells. ART kills HIV, reducing the risk of opportunistic infections and preventing the number of T-helper cells (CD4 count) dropping, in turn preventing AIDS.

In 2013, the World Health Organisation (WHO) released new recommended guidelines on antiretroviral treatment. They recommend that people start taking ART earlier than before, when their CD4 count is 500 cells/mm3, previously it was 350 cells/mm3. This is due to the wealth of benefits that are seen if people start treatment earlier, including greater success at delaying or eliminating the onset of AIDS.

Significant health gains have been noticed where treatment access has improved, especially among populations with high HIV prevalence. For example, in KwaZulu Natal province in South Africa, life expectancy has risen by 11 years since HIV treatment was scaled up in 2003. An HIV infection will cause a person's health to be compromised if they do not take antiretroviral treatment (ART). Eventually, someone living with HIV who is not taking ART will experience serious health issues and opportunistic infections, leading to AIDS.

People who are taking ART, but who do not adhere to it correctly may find that HIV becomes resistant to their treatment, allowing HIV to reproduce and multiply in their body again. This increases the risk of progressing to AIDS, and is evidence of the cause and effect relationship between HIV and AIDS.

For example, only a quarter of people living with HIV in sub-Saharan Africa have achieved viral suppression (where the level of HIV in their body has become undetectable) because of shortfalls in treatment provision or not adhering to their drugs. In 2012, 1.2 million of the 1.6 million AIDS-related deaths that year were in sub-Saharan Africa.
Even a partially effective HIV vaccine could save millions of lives. Experts have calculated that a vaccine that is 50 percent effective, given to just 30 percent of the population could reduce the number of HIV infections in the developing world by more than half over 15 years. An HIV vaccine that was more than 50 percent effective could cut the infection rate by more than 80 percent.

An HIV vaccine would have a number of key advantages over today’s HIV prevention options. In particular, the protection offered by a vaccine during sex would not depend on the consent of both partners (unlike condom use), and would not require behaviour change (unlike abstinence). An HIV vaccine would also be invaluable for couples wishing to conceive a child while minimising the risk of HIV transmission.

Children could be given an HIV vaccine before ever being exposed to HIV, and ideally this would protect them from all routes of HIV transmission. Vaccinating large numbers of people would probably require relatively little equipment and expertise, and would be much simpler and cheaper than providing antiretroviral treatment for those already infected. An HIV vaccine could be effective in either of two ways. A “preventive” vaccine would stop HIV infection occurring altogether, whereas a “therapeutic” vaccine would not stop infection, but would prevent or delay illness in people who do become infected, and might also reduce the risk of them transmitting the virus to other people. Although a preventive vaccine would be ideal, a therapeutic vaccine would also be highly beneficial.

The basic idea behind all HIV vaccines is to encourage the human immune system to fight HIV. The immune system works using a combination of cells and chemicals called antibodies. Early vaccine research focused on teaching the immune system to produce antibodies that would block HIV entering human cells. However, products designed to work this way failed in clinical trials because the antibodies worked only against lab-cultured HIV, not against the wild strains of the virus. Research has found a very small number of HIV-infected people produce 'broadly neutralising antibodies' to HIV. These antibodies, which neutralise a high percentage of the different types of HIV, are now the basis for new research into vaccine development.

Other research has focused on encouraging the immune system to produce cells to fight HIV. Nevertheless, many scientists believe such “cell-mediated” approaches will not be very effective on their own, even as therapeutic vaccines. It seems likely that a really effective vaccine will have to take a two-pronged approach involving both cells and antibodies.

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