[Effectiveness of an immunization campaign with group A and C meningococcal polysaccharide vaccine in controlling an outbreak of group C meningococcal disease].

Objective: To assess the safety, immunogenicity and efficacy of group A and C meningococcal polysaccharide vaccine (A/C MPV) in response to an outbreak of group C meningococcal disease.

Methods: A vaccination campaign with A/C MPV was prompted 6 weeks after the use of group A MPV in Laibin city, Guangxi, where an outbreak of group C meningococcal meningitis occurred in 2002. Vaccinees were observed for local and systemic reactions after the vaccination and followed up for the meningococcal disease for 5 years. Blood samples were collected from 71 people in the epidemic and 43 in the non-epidemic areas before and 1 month after the vaccination and examined by ELISA to detect IgG antibodies to group A and C polysaccharides.

Results: The vaccination coverage was 97%. No significant adverse reactions were observed. The positive rates of group C antibodies after vaccination was between 97.67% and 100% among the populations in the epidemic and non-epidemic areas, as well as among those negative and positive for group C antibodies prior to the vaccination. The geometric mean anti-C concentrations ranged 30.81 microg/ml to 37.44 microg/ml, showing no significant difference between groups. The incidence rate of meningococcal disease in students with timely immunization (218.58/100,000) dropped by 69.02%, when compared to that in those with delayed immunization (705.72/100,000). No clinical cases were identified during the follow-up period of 15,760 person-years.

Conclusion: The vaccination campaign with the Chinese group A/C MPV seemed successful in controlling the group C meningococcal outbreak. The vaccine was shown to be safe even administered after the group A vaccine only 6 weeks apart. It could induce high levels of antibodies in vulnerable population and significantly increase antibody levels in seropositive individuals, thus providing a protection of at least 5 years.