Transient elasticities of the virus population with respect to immune system parameters. During the early days of the infection the viral level is more elastic to the neutralizing antibody response parameters but as the infection progresses the viral levels are more elastic to the cell-mediated response parameters. The elasticities of the viral level to the antibody response parameters changed from negative to positive as time progressed. Thus we can conclude that neutralizing antibodies are only efficient in controlling the viral levels in the early days of the infection. The parameter values used are given in Table 1 and the initial conditions were .