Relative efficacy of different immunization schedules for the prevention of serogroup C meningococcal disease: a model-based evaluation.

Different immunization strategies have been implemented for the control of serogroup C meningococcal disease (CMD) in Canada and in other developed countries. Results from effectiveness studies of conjugate vaccines in the UK and Spain indicate waning immunity over time. To estimate the life-time protection conferred by different immunization schedules, a simulation model was constructed based on the current epidemiologic situation in Canada. Results showed that the efficacy of any immunization schedule was highly influenced by the rate at which immunity waned and that the benefit of a booster dose increased with increasing rates of waning immunity. Schedules including several doses in early infancy provided little additional benefit over programs starting with 1 dose at the age of 12 months. One-dose programs provided low levels of protection, unless the vaccine was administered at the age of 12 months, and a waning immunity rate of 1% per year or less was assumed. The most effective schedule was 5 doses given at age 2 months, 4 months, 1 year, 12 years, and 18 years, but was only marginally better than 2 doses provided at 12 months and 12 years of age. Existing routine immunization schedules may not be optimal and should be designed to achieve the highest level of protection using the lowest number of doses.