Pertussis has substantially increased in Quebec, Canada, since 1990. We estimated pertussis vaccine effectiveness and vaccine coverage in child-care centers and elementary schools.
Two retrospective cohort studies were simultaneously conducted. One included 4482 children attending 88 public child-care centers and the other included 3429 pupils in 14 elementary schools. Cough and pertussis symptoms were assessed through a questionnaire and medical records; immunization status was ascertained by examination of written records.
In child-care centers 95% of children had received at least three vaccine doses at the beginning of the follow-up; in schools more than 98% of pupils had received at least 4 doses. With ≥4 doses of vaccine and a standard case definition used for surveillance (cough ≥2 weeks, ≥1 pertussis symptom and no other apparent cause for cough), vaccine effectiveness was estimated at 61% (95% confidence interval, 44 to 72%) in child-care centers and at 60% (95% confidence interval, 10 to 82%) in schools. With the same number of doses but a case definition requiring a cough ≥5 weeks, vaccine effectiveness increased to 71% (95% confidence interval, 49 to 83) in child-care centers and to 86% (95% confidence interval, 66 to 94%) in schools.
The increase in pertussis in Quebec is not caused by a low vaccine coverage. A low vaccine effectiveness may contribute to the resurgence of pertussis in the past decade.
From Centre de Santé Publique de Québec (GDS, NB, BD, AMR) and Department of Pediatrics (PD), Université Laval and Centre Hospitalier de l'Université Laval; Public Health Unit of the Montreal General Hospital and McGill University, Montreal (RM); and Department of Pediatrics, Dalhousie University and the IWK Children's Hospital, Halifax (SH).
Accepted for publication Feb. 23, 1996.
Address for reprints: Dr. Gaston De Serres, Centre de Santé Publique de Québec, 2400 d'Estimauville, Beauport, Quebec G1E 7G9, Canada. Fax 1-418-666-2776.