Receiving a polysaccharide vaccine following a conjugate does induce an elevated antibody response but it is known that polysaccharide vaccination does not generate memory B cells and can result in the loss of the ability to mount subsequent memory antibody responses, as was observed by MacLennan et al. for Neisseria meningitidis group C anticapsular antibody responses [MacLennan et al., 2001]. The clinical importance of loss of immunological memory or induction of antibody hyporesponsiveness, is unknown. However, in addition to dampening antibody responses to a subsequent immunisation, a delay or impaired serum antibody response upon encountering an encapsulated pathogen could theoretically increase susceptibility to developing disease. Such a mechanism may explain the higher rate of otitis media observed after administration of 23-valent pneumococcal polysaccharide vaccine to Dutch children primed with a 7-valent pneumococcal polysaccharide protein conjugate vaccine as compared with the rate in controls given hepatitis B vaccine (P=0.0001) [Veenhoven et al., 2003]. In contrast, during the six months between the conjugate vaccination and booster there was a trend in favor of fewer episodes of otitis in the pneumococcal-vaccinated group.