Date: Thu, 25 Jan 2001 09:50:59 -0800
To: Mailing List
From: Croft Woodruff
Subject: JAMA Author Says Mass Immunization Not Effective Among Very Young
An article in the January 10, 2001, issue of the Journal of the American Medical Association, reports there is no evidence mass immunization is effective for controlling outbreaks or epidemics of serogroup C meningococcal disease protection in young children.
Philippe De Wals, PhD, of Sherbrooke University Hospital Center, Sherbrooke, Quebec, and colleagues studied the impact of a mass immunization campaign and assessed the vaccine effectiveness (VE) of serogroup C polysaccharide vaccine in controlling outbreaks of meningococcal disease (MCD). The authors 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 target population of the campaign was individuals aged six months to 20 years, and 84% were vaccinated. The mass immunization campaign was a response to an outbreak of MCD in Quebec province in the late 1980s. In an attempt to control this outbreak, local immunization programs directed at school aged children and adolescents were initiated in late 1991 and extended in 1992. By the autumn 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. As a result, 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 registered.
The study found that vaccine effectiveness was strongly related to the age of the individual at the time of vaccination, for children aged two to nine years, VE was 41%. "There was no evidence of protection in children younger than two years; all eight MCD cases in this age group occurred in vaccines," De Wals et al. reported. "Ultimately, cost effectiveness should be the criterion for deciding which of the polysaccharide or conjugate vaccines should be recommended for different age groups. Results of randomized trials and epidemiological 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 young than two years," De Wals' group concluded.