An immunogenic composition comprising a plurality of capsular polysaccharides from Streptococcus pneumoniae serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F and 23F conjugated to a carrier protein, and further comprising at least one preservative, preferably 2-phenoxyethanol (2-PE). The preservative-containing immunogenic compositions of the invention confer resistance to one or more micro-organisms and are useful for producing multi-dose vaccine formulations having advantageous properties with respect to long term stability of the different antigenic determinants in the immunogenic composition of choice. Related compositions and methods for measuring the efficacy of one or more preservatives in a vaccine formulation are also provided.
