Mass Immunization Has Limited Benefits.(Quebec mass immunization against meningitis reports mixed results)

2001 MAR 7 - (NewsRx.com & NewsRx.net) --

by Michelle Marble, staff medical writer -- Researchers in Canada report mixed results from a massive immunization campaign against meningitis in that country.

During the winter of 1992-1993, a mass immunization campaign was conducted in Quebec. The target population was residents aged six months to 20 years. During the campaign, 84% of the target population (approximately 1.9 million individuals) was vaccinated.

For the study, P. Dewals and colleagues at University of Sherbrooke analyzed the meningococcal disease (MCD) cases reported in Quebec from 1990 to 1998, encompassing the time before, during, and after the immunization campaign. Dewals et al. published their study in the Journal of the American Medical Association.

They determined the overall incidence of MCD between 1990-1998 as well as the incidence of culture-proven serogroup C MCD between April 1, 1993, and March 31, 1998. They then compared the data among vaccinated and unvaccinated persons in the target population.

"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)," reported Dewals et al.

The vaccine campaign resulted in protection from serogroup C MCD in the first two years after vaccine administration (vaccine effectiveness (VE), 65%; 95% confidence interval [CI], 20%-84%). However, protection did not continue into the next three years (VE, 0%; 95% CI, -5% to 65%), the researchers said.