Multiple infection
Unlike some other viruses, infection with HIV does not provide immunity against additional infections, in particular, in the case of more genetically distant viruses. Both inter- and intra-clade multiple infections have been reported,[63] and even associated with more rapid disease progression.[64] Multiple infections are divided into two categories depending on the timing of the acquisition of the second strain. Coinfection refers to two strains that appear to have been acquired at the same time (or too close to distinguish). Reinfection (or superinfection) is infection with a second strain at a measurable time after the first. Both forms of dual infection have been reported for HIV in both acute and chronic infection around the world.[65][66][67][68]
Prevention
A course of antiretroviral treatment administered immediately after exposure, referred to as post-exposure prophylaxis, reduces the risk of infection if begun as quickly as possible.[69] In July 2010, a vaginal gel containing tenofovir, a reverse transcriptase inhibitor, was shown to reduce HIV infection rates by 39 percent in a trial conducted in South Africa.[70] Early treatment of HIV-infected people with antiretrovirals protected 96% of partners from infection.[71] Testing post exposure is recommended initially and at six week, three months, and six months.[72]
There is currently no publicly available vaccine for HIV or AIDS.[73][74][75] However, a vaccine that is a combination of two previously unsuccessful vaccine candidates (ALVAC-HIV and AIDSVAX) was reported in September 2009 to have resulted in a 30% reduction in infections in a trial conducted in Thailand.[76][77] Further trials of the vaccine are ongoing.[78][79]
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