This study is a continued evaluation of the immune response to StaphVAX , a Staphylococcus aureus type 5 and 8 capsular polysaccharide conjugate vaccine, in end-stage renal disease patients, by giving a 3rd and 4th dose to a subset of the participants in the previous efficacy trial. Participants continue to receive the vaccine or placebo in a blinded manner, and are also randomly assigned to 1 of 2 different intervals between the doses. The immunogenicity is measured by the antibodies in the blood, and typical vaccine safety information is also collected.