Priscilla Luna, left, and her 3 year-old daughter, read a book about immunizations at a vaccine clinic in Lubbock, Texas, on March 1. Cases of measles are on the rise in Texas and in southwestern Ontario.

Measles is so infectious that when under-vaccinated individuals mingle, they'll always be at risk. That's why public health officials across Canada stress the importance of high vaccination rates amid backsliding and growing outbreaks.