Impact of a Mass Immunization Campaign against Serogroup C Meningococcus in the Province of Quebec, Canada

Article excerpt


The number of reported cases of meningococcal disease in Quebec has been increasing over recent years: from 37 in 1984, 62 in 1986, 107 in 1988, to 124 in 1990. This change was associated with the emergence of a virulent clone of Neisseria meningitidis, serogroup C, serotype 2a (1). Outbreaks caused by serogroup C organisms have also been observed in other parts of Canada and the USA (2, 3). Since 199O, the epidemiology of serogroup C meningococcal disease in Quebec has been characterized by an unusually high attack rate among teenagers and a high fatality rate (15%). The disease incidence was higher in some areas of Quebec Province (e.g., Hull) than others (Quebec city and Montreal). At regional level, there was a tendency for the cases to be clustered in time and space although few secondary cases were seen among direct contacts of patients.

In an attempt to control this outbreak, local and regional immunization programmes directed at school-age children were initiated in late 1991 and continued in 1992. In the autumn of 1992, approximately 300000 doses of polysaccharide vaccine had been administered but the incidence remained high in unvaccinated groups and clusters appeared in previously unaffected areas. This provoked enormous anxiety in the population, fuelled by the media. As a result, it was decided to conduct a mass immunization programme and to offer the vaccine free of charge to all the 1.8 million persons living in the province who were aged between 6 months and 20 years. This intervention started in December 1992 and was completed by the end of March 1993, mainly through the local health units of the public health service.

This article describes the vaccination coverage achieved at the end of the programme and evaluates the costs and benefits in terms of cases prevented.

Study population and methods

The study population encompassed all persons living in the Province of Quebec. The size of the population and its age distribution were estimated from projections based on the 1991 census. During the mass immunization campaign, in early 1993, a central vaccination registry was created by linking the provincial health insurance file with the individual vaccination forms returned by the local health units. The number of vaccinees in each single age category was extracted from the registry (n = 1174957) and corrections were made for the forms not matching an individual in the health insurance file (n = 2362), for the vaccines provided by the private sector (n = 12003), and for vaccines administered in 1991-92 and not recorded (n = 435471), using a distribution proportional to age.

The overall cost of the programme was calculated from the purchases of vaccines made by the Ministry of Health, including the doses given to the private sector, and the ordinary and extra resources used by the provincial, regional and local public health services to promote, organize, carry out and evaluate the immunization campaigns. The additional expenses incurred by the provincial health insurance plan for the participation of physicians was estimated as a three-day fee per 1000 persons vaccinated. Costs are expressed in 1993 Canadian dollars (CAD).

Since 1990, reportable diseases have been centrally registered at the provincial level and standard case definitions are provided (4). When a case of invasive meningococcal infection is reported by a clinician or a laboratory, an investigation is conducted by the regional health authority in order to collect additional information, including the date of occurrence of the disease, confirmation of the diagnosis, the serogroup of the bacteria, and the vaccination status of the patient. The sources of information include the hospital, the laboratory, and patients or their families. Cases occurring between 1 January 1990 and 31 March 1994 have been included in this analysis. Clinical cases and confirmed cases of unknown serogroup were ascribed to the different serogroups according to a proportion specific for the age, year, and vaccination status. …