G. Deserres et al., EFFECTIVENESS OF A WHOLE-CELL PERTUSSIS-VACCINE IN CHILD-CARE CENTERSAND SCHOOLS, The Pediatric infectious disease journal, 15(6), 1996, pp. 519-524
Background. Pertussis has substantially increased in Quebec, Canada, s
ince 1990, We estimated pertussis vaccine effectiveness and vaccine co
verage in child-care centers and elementary schools. Methods. Two retr
ospective cohort studies were simultaneously conducted, One included 4
482 children attending 88 public child-care centers and the other incl
uded 3429 pupils in 14 elementary schools. Cough and pertussis symptom
s were assessed through a questionnaire and medical records; immunizat
ion status was ascertained by examination of written records. Results.
In child-care centers 95% of children had received at least three vac
cine doses at the beginning of the follow-up; in schools more than 98%
of pupils had received at least 4 doses. With greater than or equal t
o 4 doses of vaccine and a standard case definition used for surveilla
nce (cough greater than or equal to 2 weeks, greater than or equal to
1 pertussis symptom and no other apparent cause for cough), vaccine ef
fectiveness 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 requir
ing a cough greater than or equal to 5 weeks, vaccine effectiveness in
creased to 71% (95% confidence interval, 49 to 83) in child-care cente
rs and to 86% (95% confidence interval, 66 to 94%) in schools. Conclus
ions. The increase in pertussis in Quebec is not caused by a low vacci
ne coverage. A low vaccine effectiveness may contribute to the resurge
nce of pertussis in the past decade.