CD4 and diphtheria: Vaccine-induced immune responses following tetanus vaccination appear to be similar in both HIV-infected and HIV-uninfected individuals.44 In contrast, vaccine-induced immune responses following diphtheria vaccination are lower in the presence of HIV infection and are influenced by the CD4+ counts.7 Studies show that following primary vaccination with tetanus and diphtheria vaccines among HIV-infected children, there is a quick waning of the vaccine-induced immunity.45