Two new cases of the measles have been confirmed in Calgary.
Alberta Health Services says the two cases are linked and are not travel related.
Western Canada High School has a note to parents on its website about the possible exposure.
It says AHS will directly contact families if there are questions on whether a student is immune or adequately protected against measles. Health officials are concerned with those who were at the school between 9 a.m. and 12:30 p.m. MT on March 31.
Calgary's Medical Officer of Health will provide more details at a news conference on Thursday.
A warning of a possible measles exposure at Western Canada High School was also issued in January.
In October and November, Alberta Health Services said there were 40 cases of measles in AHS's South zone, which does not include Calgary.