Individuals homozygous for a 32-basepair deletion mutation (null mutation) in CCR5, a chemokine receptor, are nearly immune to developing HIV infection. Recently based on molecular dating evidence it has been proposed that the bacterium Yersinia pestis, cause of plague, may have been the selective pressure which selected for a high prevalence of the 32-basepair null mutation. An association of a robust chemokine response with HIV vaccine efficacy has recently been shown. I suggest that Y. pestis may be a useful adjuvant in an HIV vaccine protocol by stimulating a vigorous chemokine response.