HIV superinfection rates are high, suggesting HIV vaccination approaches might not be effective.
HIV superinfection occurs when individuals who are already infected with HIV contract a new strain of HIV which is phylogenetically different from the previous strain. HIV superinfection has several important clinical implications . At an individual level, it has been shown that HIV superinfection can lead to poor HIV control even in patients who were previously controlling their HIV infection. From a public health perspective, a finding of high superinfection rates suggests that the host immune responses to primary HIV infection do not confer resistance to reinfection with a different strain and any vaccine strategy aimed at utilizing the natural anti HIV immune responses may not be very effective.
Study of HIV superinfection rates
The results of one of the first large scale studies looking at the rates of HIV superinfection show some surprising results. The study, published in the June issue of the Journal of Infectious diseases, shows that HIV superinfection is occurring at a similar rate as compared to primary HIV infection. This is in contrast to previous studies which have reported low rates of superinfection. Researchers believe that the low sensitivity assays used to detect superinfection in these previous studies led to the deceptively low rates. The current study is also unique because it looks at superinfection rates in a general heterosexual population (previous studies have included only patients with high risk behaviors). The sample population was a cohort of individuals between the ages of 15-49 in the Rakai district in southwestern Uganda. To identify HIV superinfection, viral RNA was examined from HIV positive individuals at baseline (time of initial HIV diagnosis) and then compared to samples obtained from the same individuals at a later point of time (median time to follow-up was 2 years). Using genomic techniques, researchers amplified 2 regions of the HIV virus- the p24 region of the viral capsid and the gp41 region of the viral envelope and compared the sequences for each subject from baseline to the second sample.
Based on the RNA sequencing of these regions, patients were found to either have no superinfection or have a superinfection with a new strain which was within the original subtype (infrasubtype) or a completely different subtype (intersubtype). From the 149 individuals examined, 7 were found to have acquired a new HIV strain that was genomically different from the baseline strain. There was no significant change noted in the patient’s HIV viral loads despite superinfection. Researchers then compared the incidence of HIV superinfection to primary HIV infection in HIV negative individuals during the same time period and concluded that the rates were equivalent.
Limiting factors of the study included the small sample size. In addition, samples for analysis were obtained before patients initiated anti-retroviral therapy, which is known to decrease the risk of HIV transmission.
Implications of HIV vaccines
With the growing emphasis on creating a successful HIV vaccine in recent years, the results of this study pose some interesting challenges to researchers. If the host immune response to primary HIV infection is not sufficient to protect against reinfection with a different strain, vaccines which hope to utilize the same host immune responses to garner protection are likely to be ineffective. On the flip side, the study also showcases a subset of the population which was protected from superinfection and provides an interesting subgroup of individuals for researchers to explore.
Redd, Andrew D. et al. The Rates of HIV Superinfection and Primary HIV Incidence in a General Population in Rakai, Uganda. Journal of Infectious Diseases, June, 2012.
Stem cell therapy approaches to HIV. An update on basic-science HIV research.