Effectiveness of a mass immunization campaign against serogroup C meningococcal disease in Quebec.
BACKGROUND
An outbreak of meningococcal disease in Quebec province prompted a mass immunization program. The impact of this campaign on the epidemiology of meningococcal disease has not been studied.


OBJECTIVE
To study the impact of a mass immunization campaign using polysaccharide vaccine on the epidemiology of meningococcal disease (MCD) and to assess serogroup C vaccine effectiveness (VE).


METHODS
Analysis of MCD cases reported in Quebec from 1990 to 1998, before and after the mass immunization campaign was conducted during the winter of 1992-1993, when 84% of residents aged 6 months to 20 years (the target population, approximately 1.9 million individuals) were vaccinated.


METHODS
Incidence of MCD in 1990-1998; incidence of culture-proven serogroup C MCD between April 1, 1993, and March 31, 1998, compared among vaccinated and unvaccinated persons in the target population.


RESULTS
The incidence of serogroup C disease decreased after the mass immunization campaign, from 1.4 per 100 000 in 1990-1992 to 0.3 per 100 000 in 1993-1998, and the overall incidence of other serogroups remained stable at 0.7 per 100 000, with a small increase in the proportion of cases caused by serogroup Y (P =.009). Protection from serogroup C MCD was indicated in the first 2 years after vaccine administration (VE, 65%; 95% confidence interval [CI], 20%-84%), but not in the next 3 years (VE, 0%; 95% CI, -5% to 65%). Vaccine effectiveness was strongly related to age at vaccination: 83% (95% CI, 39%-96%) for ages 15 through 20 years, 75% (95% CI, - 17% to 93%) for ages 10 through 14 years, and 41% (95% CI, -106% to 79%) for ages 2 through 9 years. There was no evidence of protection in children younger than 2 years; all 8 MCD cases in this age group occurred in vaccinees.


CONCLUSIONS
Serogroup C polysaccharide vaccine is effective for controlling outbreaks in teenaged individuals but should not be used in children younger than 2 years. The mass campaign did not induce significant serogroup switching.
De Wals
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Département des sciences de la santé communautaire, Université de Sherbrooke, 3001 12th Ave N, Sherbrooke, Quebec, Canada J1H 5N4. pdewals@courrier.usherb.ca
De Serres
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Niyonsenga
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D000293:Adolescent; D000328:Adult; D000942:Antigens, Bacterial; D002648:Child; D002675:Child, Preschool; D006801:Humans; D017589:Immunization Programs; D015994:Incidence; D007223:Infant; D016015:Logistic Models; D008589:Meningococcal Infections / Q000453:epidemiology* / Q000517:prevention & control*; D022401:Meningococcal Vaccines / Q000008:administration & dosage*; D009345:Neisseria meningitidis / Q000145:classification / Q000276:immunology; D011135:Polysaccharides, Bacterial; D011792:Quebec / Q000453:epidemiology; D012703:Serotyping
D000942:Antigens, Bacterial; D022401:Meningococcal Vaccines; D011135:Polysaccharides, Bacterial; C037676:meningococcal group C polysaccharide