Herd immunity from meningococcal serogroup C conjugate vaccination in England: database analysis

In November 1999, the United Kingdom introduced routine meningococcal serogroup C conjugate vaccination for infants. The vaccine was also offered to everyone aged under 18 years in a phased catch-up programme.1 The first to be vaccinated were adolescents, and the entire programme was completed by the end of 2000. On the basis of direct protection provided by the vaccine, 1 2 this catch-up programme was likely to be cost effective.3 Maiden et al described a 67% reduction (from 0.45% to 0.15%) in the prevalence of nasopharyngeal carriage of serogroup C meningococci in adolescents before and after the vaccination programme.4 A fall in meningococcal carriage would be expected to reduce exposure among unvaccinated children and therefore to enhance the effectiveness of meningococcal conjugate vaccine. We present rates of disease in vaccinated and unvaccinated children to provide the first evidence of an indirect effect from meningococcal conjugate vaccine. Since December 1999 we have investigated the vaccination history of all cases of …