Effectiveness of a mass immunization campaign using serogroup C meningococcal conjugate vaccine.

Context: Meningococcal polysaccharide vaccines are of limited effectiveness. New protein-polysaccharide conjugate vaccines have yet to be evaluated in field conditions.

Objective: To assess the effectiveness of a serogroup C conjugate meningococcal vaccine in an outbreak setting.

Design, Setting, And Participants: Population-based observational study of cases of invasive serogroup C meningococcal disease from 1996 through 2002 in Quebec identified from the provincial registry of notifiable diseases and from the provincial reference laboratory. In 2001, a mass immunization campaign with a conjugate vaccine was conducted to control an emerging epidemic. The number of vaccinated individuals was extracted from meningococcal immunization registries.

Main Outcome Measures: Incidence of invasive meningococcal disease before and 1 year after the campaign in vaccinated and unvaccinated individuals.

Results: Vaccination coverage of those 2 months to 20 years was 82.1%. After the campaign, the number of cases of serogroup C disease decreased from 58 in 2001 to 27 in 2002, and the incidence from 7.8 per million to 3.6 per million. Vaccine effectiveness was found to be 96.8% (95% confidence interval, 75.0%-99.9%). There was no observed increase in the incidence of the other serogroups.

Conclusion: The new conjugate vaccine was effective in controlling an emerging epidemic of serogroup C meningococcal disease, as well as providing short-term protection across a wide age range.