This is the finding of a study reported in today's issue of the Journal of the American Medical Association (JAMA).

Philippe De Wals, Ph.D., of Sherbrooke University Hospital Center, Sherbrooke, Quebec, and colleagues studied the effect of a mass immunization campaign and assessed the vaccine effectiveness (VE) of serogroup C polysaccharide vaccine in controlling outbreaks of meningococcal disease (MCD).

They analyzed MCD cases reported in Quebec from 1990 to 1998, before and after the mass immunization campaign was conducted during the winter of 1992-1993. The campaign was aimed at individuals aged six months to 20 years, and 84 percent were vaccinated.

The campaign was a response to an outbreak of MCD in Quebec province in the late 1980s.

In an attempt to control the outbreak, local immunization programs directed at school-aged children and adolescents were initiated in late 1991, and extended in 1992. By fall of that year, approximately 300,000 doses of polysaccharide vaccine had been administered, but the incidence of serogroup C MCD continued to stay high in the groups that were not vaccinated, and clusters appeared in previously unaffected areas.

Responding to these findings, local authorities decided to conduct a mass immunization program and to offer the vaccine free to all 1.9 million people living in the province between the ages of six months and 20 years.

The campaign started in December 1992 and was completed by the end of March 1993. Approximately 1.6 million doses of vaccine were distributed. During the period from January 1, 1990 through December 31, 1998, a total of 899 MCD cases were discovered.

"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," the authors report in the JAMA article.

"Protection from serogroup C MCD was indicated in the first two years after vaccine administration (VE, 65 percent), but not in the next three years (VE, 0 percent)," they continue.

Vaccine effectiveness was strongly related to the age of the individual at the time of vaccination, with the strongest effectiveness among the older individuals. For those aged 15 through 20 years, VE was 83 percent; for those aged 10 through 14 years, VE was 75 percent; and for children aged two to nine years, VE was 41 percent.

"There was no evidence of protection in children younger than two years; all eight MCD cases in this age group occurred in vaccinees," the authors report.

"Ultimately, cost-effectiveness should be the criterion for deciding which of the polysaccharide or conjugate vaccines should be recommended for different age groups," they write. "Results of randomized trials and epidemiologic studies on conjugate vaccines are urgently needed for comparison purposes."

"Serogroup C polysaccharide vaccine is effective for controlling outbreaks in teenaged individuals but should not be used in children younger than two years," the authors conclude.

The study was carried out with the support of the Ministere de la sante et des services sociaux du Quebec and the Institut national de la sante publique du Quebec. (JAMA. 2001; 285:177-181)

10-Jan-2001