Health officials in Metro Vancouver confirmed late last month that one boy and one girl were diagnosed with the highly contagious disease shortly after returning from a school trip over spring break.
Deputy provincial health officer Dr. Bonnie Henry says in an email that two more cases were diagnosed on Wednesday and those people were on the same trip.
She says medical officials can't determine if everybody was infected from a common source because of the incubation period.
Measles can be airborne for up to two hours after an infected person leaves the area, and does not require direct face-to-face contact for transmission.
Serious complications like inflammation of the brain and brain damage, convulsions and deafness can result from the highly infectious illness.
Hundreds of measles cases broke out in B.C.'s Fraser Valley in 2014, but only 17 cases were confirmed in the province in 2013.
Doctors across Canada have been urging the public to get vaccinated after outbreaks in Quebec and Ontario over the past several months.
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