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The importance of primary HIV infection in sustaining the HIV epidemic.
Koopman JS; Jacquez JA; Simon CP; Adams A; Foxman B; Lange K; Pollock S;
November 30, 1996
3rd Conf Retro and Opportun Infect. 1996 Jan 28-Feb 1;:176. Unique

Background: The contagiousness of HIV infection is concentrated into primary and late stages of infection. The importance of these stages in the HIV epidemic is a function of both 1) the amount of virus excreted and 2) how transmissions are connected into chains. Methods: HIV spread through homosexual populations was analyzed using models where individuals progress through sequential sexual life stages and, if infected, through sequential stages of infection. Partnership formation rates were set to rise then fall with age. Individuals formed partnerships preferentially with others of their own age. Twenty percent or less of total virus was excreted during primary infection. Results: Reducing contagiousness during primary infection slowed epidemics hundreds of times more than equal reductions in late stage infection. Eliminating all transmissions during primary infection stopped viral spread. Eliminating all transmissions from late stage infection reduced the endemic level of infection by less than half. This dominance of primary infection was evident even given conservative parameter values. Conclusions: The way transmissions during different stages of infection are connected into chains allows transmissions during primary infection to dominate the spread of infection even when the amount of virus excreted during primary infection is only a small fraction of all virus excreted. Consequently, vaccines which fail to prevent infection but which reduce contagiousness during primary infection have the potential to stop the HIV epidemic.