Thanks for the full study.
Here is my interpretation of the wrong city issue.
"Data on MMR uptake for the study period were available through the Direction de Sante ́ Publique de la Capitale Nationale (N. Boulianne, BN, MSc, written communication, 2005). These data were routinely collected in the region of Quebec
among 5-year-old children attending kindergar- ten during the years 1993-2004 (ie, for birth cohorts
from 1988 –1998). Vaccination records from children were used as the main source of information to docu- ment MMR vaccination and its date. When this infor- mation was not available, vaccination status of the chil- dren was obtained through consultation of the regional vaccination registry or else through direct contact with doctor’s practices, both from community clinics or pri- vate offices. Data were unavailable for 2 birth cohorts (1987 and 1997) during the study interval. Surveys were performed annually on a total population of 35 643 children, with each annual sample fluctuating in size between 2234 in 1990 to 5914 in 1993. For the 10 birth cohorts with available data, the average MMR uptake in Quebec was 93.2% during the whole period, ranging from 91.3% in the 1992 birth cohort to 96.4% in the 1989 birth cohort."
MMR uptake records were housed in Quebec City. No biggie. That is the province's capital. The records though are either largely drawn from Quebec City or from the Province of Quebec as a whole....and that is a huge problem. I tend to think the vaccine records were drawn from Quebec City and area, as why would they bother to say "Quebec Region" if they meant the whole province?
This is a huge issue. I cannot stress how different Montreal is from Quebec City and indeed, the rest of the province. Quebec City is 94% French Canadian, with a small smattering of Anglos and immigrants.
Quebec as a whole outside of Montreal has low genetic diversity - here is a link that discusses Quebec and founder populations.
Montreal, OTOH, is extremely diverse.