The Influence of Treatment- and Vaccination-induced Changes in the Risky Contact Rate on HIV Transmission

The influence of treatment- or vaccination-induced changes in the risky contact rate (RCR) on HIV transmission in the homosexual population of San Francisco is investigated, given the heterogeneous susceptibility and progression rates of the mutant allele CCR5 Δ32. Susceptible individuals have no, partial, or complete immunity against HIV. Some susceptible newcomers are vaccinated. Infected individuals have a slow, a normal, or a rapid progression rate. Some newly infected individuals are treated. Vaccinated and treated individuals may change the RCR, the influence of which is quantified by the change in the basic reproductive numbers obtained from differential equations. If vaccination increases (decreases) the RCR, the epidemic will decrease (increase). If the treatment increases (decreases) the RCR, the epidemic will increase (decrease). The influence of treated individuals is much higher than the influence of vaccinated individuals. Prophylactic effort should be devoted more to preventing an increase of the RCR in treated individuals than to preventing a decrease of the RCR in vaccinated individuals.basic reproductive number, contact rate, HIV transmission, homosexual, treatment, vaccination,