Carrier-induced epitopic suppression is of particular concern where multiple conjugates with the same carrier protein are administered simultaneously. To avoid the suppression, the invention minimizes the amount of unconjugated carrier protein in a vaccine. The invention provides a composition for immunizing a patient against a disease caused by Neisseria meningitidis, wherein (1) the composition comprises conjugates for at least two of the four meningococcal serogroups A, C, W135 and Y, where at least two of the conjugates have a common carrier protein; and (2) the composition includes the common carrier in an unconjugated form at less than 10 μg/ml.