Low pertussis toxin antibody levels in two regional cohorts of Canadian pregnant women.

•Pertussis toxin antibody (anti-PT) was assessed in Canadian antenatal cohorts from 2013 to 1996–1997.•59% of a 2013 antenatal cohort had undetectable anti-PT (<10 ELISA units/ml).•51% of a 1996–1997 antenatal cohort in British Columbia had undetectable anti-PT (<10EU/ml).•A majority of Canadian pregnant women studied is likely susceptible to pertussis disease.•Most newborn infants will also likely be susceptible to pertussis disease until gaining vaccine protection.