Session 51Poster Presentations Novel Vaccine Approaches Session Day and Time: Thursday 1:30 - 3:30 pm Room: Hall D
433 AIDS Vaccines That Allow HIV-1 to Infect and Escape Immunological Control: A Mathematical Analysis of Mass Vaccination J. A. Bogaards*1, M. van Ballegooijen2, M. C Boerlijst2, G-J. Weverling1, J. Goudsmit3 1Academic Med Ctr, Univ of Amsterdam, The Netherlands; 2Section Population Biology, Univ of Amsterdam, The Netherlands; and 3Ctr for Poverty-related Communicable Diseases, Amsterdam, The Netherlands
Background: HIV vaccine concepts shown to reduce viremia and postpone disease, but not prevent infection in monkeys, are currently in human Phase I trials. The key question is if widespread application of such vaccines could have a significant impact on the AIDS epidemic in the developing world. To study their potential effect on the AIDS epidemic, we modeled the spread of HIV-1 and progression to AIDS in a population of sexually active individuals.
Methods: We designed a mathematical model, formulated in differential equations, that correlates the level of viremia to disease progression in individuals and to transmission from infected to uninfected individuals in a population. Parameters for disease progression were estimated from longitudinal data on 695 HIV-1 infected participants of the Amsterdam Cohort Studies on HIV infection and AIDS. Viral escape and disease progression in vaccinees were assumed to proceed as in untreated HIV-1 infected individuals with the best prognosis, e.g., natural slow progressors. Parameters for risk of virus transmission were derived from the literature.
Results: We calculated an average time from HIV-1 acquisition to the onset of AIDS of 9.2 yrs (12.2 yrs for those with the best prognosis). If each HIV-1-infected individual would transmit the virus to 5 others in case all sexual contacts were with uninfected individuals (e.g., R0 = 5), the sexually active population can be reduced to 25% of its initial size as a result of AIDS-induced mortality in absence of vaccination or treatment against HIV-1. Mass vaccination using a viremia-reducing vaccine when HIV-1 prevalence is still low (0.1% of population infected) will postpone and lower the peak of the HIV-1 epidemic. It will retard by as much as 20 yrs the epidemic stage at which the sexually active population shrinks rapidly due to AIDS-induced mortality. Despite inducing a longer chronic infection phase, it seems likely to result in a slightly decreased overall HIV-1 transmissibility (R0<5). However, the later vaccination is initiated in an epidemic, the less it will curb the spread of HIV-1, until its only impact is the improved prognosis of HIV-1-infected vaccinees.
Conclusions: AIDS vaccines allowing HIV-1 to infect and escape immunological control are beneficial to the vaccinees, independent of the stage of the epidemic; however, the number of long-term survivors is substantially increased only when vaccination is initiated early in the epidemic.
