The present invention relates to in vitro methods for producing Neisseria meningitidis capsular polysaccharides which have a defined length. The present invention also relates to compositions comprising at least one capsule polymerase, at least one donor carbohydrate and at least one acceptor carbohydrate, wherein the ratio of donor carbohydrate to acceptor carbohydrate is a ratio from 10:1 to 400:1. Moreover, the present invention provides truncated versions of the capsule polymerases of Neisseria meningitidis serogroups A and X. Also provided herein are pharmaceuticals, in particular vaccines, comprising the synthetic capsular polysaccharides of Neisseria meningitidis which have a defined length. Furthermore, the invention provides for methods for the production of said vaccines.
