A measles outbreak
in a population with 99.0% vaccination
coverage. The authors state, "Incomplete vaccination
coverage is not a valid explanation for the Quebec City measles outbreak
Boulianne N, De Serres G, Duval B, Joly JR, Meyer F, Déry P, Alary M, Le Hénaff D, Thériault N. Département de santé communautaire, Centre Hospitalier de l'Université Laval. [Major measles epidemic in the region of Quebec despite a 99% vaccine coverage] [Article in French]. Can J Public health. 1991 May-Jun;82(3):189-90
The 1989 measles outbreak in the province of Quebec has been largely attributed to an incomplete vaccination coverage. In the Quebec City area (pop. 600,000) 1,363 confirmed cases of measles did occur. A case-control study conducted to evaluate risk factors for measles allowed us to estimate vaccination coverage. It was measured in classes where cases did occur during the outbreak. This population included 8,931 students aged 5 to 19 years old. The 563 cases and a random sample of two controls per case selected in the case's class were kept for analysis. The vaccination coverage among cases was at least 84.5%. vaccination coverage for the total population was 99.0%. Incomplete vaccination coverage is not a valid explanation for the Quebec City measles outbreak.
And here is a CDC bulletin (MMWR, May 12, 1989 / 38(18);329-330):
Since late December 1988, more than 1600 cases of measles have been reported in the province of Quebec, Canada. Five hundred of the cases have occurred in metropolitan Montreal. In 199 (40%) of these cases, the onset of rash occurred in April (Figure 1). Detailed information is available for 486 (97%) of the 500 Montreal cases. Of these, 104 (21%) occurred in preschoolers aged 0-4 years, 328 (67%) in school- aged persons 5-19 years of age, and 54 (11%) in adults greater than or equal to 20 years of age. Of the adults, 42 (78%) were aged 20-29 years. Of school-aged patients, 191 (58%) had histories of previous vaccinations. From January through March, "Operation Mise a jour" (Operation Update) was conducted in Montreal to ensure that all primary and secondary school students were adequately vaccinated against measles. Before this campaign, approximately 50,000 of the 285,000 Montreal primary and secondary school students lacked documentation of vaccination. During the campaign, approximately 30,000 (60%) of these students were vaccinated. Reported by: RS Remis, MD, L Bedard, MScN, R Palmer, Bureau regional des maladies infectieuses; Les departements de sante communautaire du Regroupement de DSC du Montreal metropolitain; Centres locaux de services communautaires du Montreal metropolitain, Montreal; PM Lavigne, MD, Provincial Epidemiologist, Quebec City, Quebec; Laboratory Centre for disease Control, Ottawa, Ontario, Canada. Div of immunization, Center for Prevention Svcs, CDC.