HIV superinfection, also known as "doubling down", is a condition in which a person with established human immunodeficiency virus infection acquires a second strain of the virus. The second strain co-exists with the first and may cause more rapid disease progression or carry resistance to medicines.
People with HIV risk superinfection by the same actions that would place a non-infected person at risk of acquiring HIV. These include sharing needles and forgoing condoms with HIV-positive sexual partners. For many years superinfection was thought to occur mainly in high-risk populations. However, research from Uganda published in 2012 demonstrated that HIV superinfection occurs at a similar rate to the rate of primary HIV infection in a general heterosexual population. In addition, preliminary results of female bar workers in Kenya presented at the 2012 Conference of Retroviruses and Opportunistic Infections by researchers at the Fred Hutchinson Cancer Research center also found that HIV superinfection occurs at a similar rate to primary HIV infection.
Immunology of HIV Superinfection It is unknown what aspects of the natural immune response to HIV may protect someone from superinfection, but it has been shown that cytotoxic lymphocyte responses do not seem to be protective. In addition, it has been demonstrated that superinfection can occur in individuals that demonstrate a robust anti-HIV antibody response. Interestingly, the anti-HIV antibody response broadens and strengthens in individuals post-superinfection. Taken with the finding that super-infection is common and occurs within and between HIV subtypes it has been suggested that the immune response elicited by primary infection may confer limited protection and raises concerns that HIV-vaccine strategies designed to replicate the natural anti-HIV immune response may have limited effectiveness in preventing new infections. However at the same time, HIV-infected individuals at high-risk for super-infection who do not become superinfected may also provide a very interesting avenue for new vaccine research.
HIV Co-infection Offset A study in the New England Journal of Medicine titled 'Inhibition of HIV-1 Disease Progression by Contemporaneous HIV-2 Infection' revealed that people who are HIV+ with the two major subtypes actually have a slower progression towards AIDS than people with only HIV1 or HIV2. This challenges the notion of Super-infection by illustrating that contemporaneous infection can actually offset itself.
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