Laboratory staff at Manchester have not received a Hib vaccine although they have received a number of meningococcal vaccines with the majority having received their meningococcal serogroup C conjugate vaccine in 1999. Certain staff would have received bivalent meningococcal A and C prior to the conjugate vaccine which has recently been demonstrated to hinder the induction of immunological memory by the conjugate vaccine [Vu et al., 2006]. Following the conjugate vaccine many staff have since received a quadrivalent A/C/Y/W135 polysaccharide vaccine in the following seven years, but little is known about the duration of protection in this age group.