6th Canadian Immunization Conference

Oral Scientific Abstracts
Palais des congrès
Montréal, Québec
5 to 8 December, 2004

The scientific poster and oral presentations is one of the major scientific components of the Canadian Immunization Conference which was held at the Palais des congrès in Montreal, Quebec on 5 to 8 December, 2004. Prior to the conference, scientific abstracts were submitted and evaluated by the Scientific Subcommittee. The best abstracts were chosen for presentation at the conference. This year, there were 75 posters and 12 oral presenters; six have expressed an interest in publishing their abstacts in the Canada Communicable Disease Report (CCDR).


Category: Bacterial Vaccines or Infections

Epidemiology of Hospitalized Pertussis After Change From Whole-Cell to Acellular Pertussis Vaccine

Bettinger JA, Halperin SA, De Serres G, Scheifele D, Tam T

Background and Purpose

Between July 1997 and April 1998, all provinces and territories in Canada changed from universal infant immunization with a whole-cell pertussis-containing vaccine (WCV) to an acellular pertussis containing vaccine (ACV). The purpose of this analysis was to determine whether there was a change in the epidemiology of hospitalized pertussis following this nationwide program change.

Methods

The IMPACT pertussis database was examined for all cases of pertussis from January 1991 through June 2004. IMPACT is an active surveillance network in 12 pediatric centres in Canada that account for approximately 90% of the pediatric tertiary care beds in the country. Rates and characteristics of hospitalized cases of pertussis were compared between theWCV and the ACV eras.

Results

A total of 2,000 cases of pertussis were admitted to IMPACT centres during the 13.5-year period; 121 cases were vaccinated or born during the transition period and were not included in the analysis. Specific immunization information was available on 891 (44.6%) and was inferred by the immunization date on the remainder. There were 1,171 cases in theWCV and 708 in the ACV era with a slight female predominance in both the WCV and ACV eras (54.3% and 51.3%). Most cases occurred in the 6-month period from July to December (66.3% and 62.5%). There was a significant shift in age distribution with a higher proportion of infants either too young to be immunized (0 to 1 month; 42.5% in ACV vs. 27.5% WCV) or too young to have received two doses (2 to 3 months; 41.5% vs. 32.6%). A significantly lower proportion of hospitalized infants in the ACV era were old enough to have received two doses (4 to 6 months; 11.9% in ACV vs. 19.5% in WCV) or three doses (7 to 11 months; 1.7% vs. 8.1%). The proportion of infants admitted in the second year of life was also significantly lower in the ACV era (1.7% vs. 9.2%). Vaccine failures were more common in the WCV (13.2%) than the ACV (2.8%) era. No differences were found in duration of ICU or hospital stay.

Conclusion

The change from WCV to ACV has been associated with a shift toward younger, unimmunized or incompletely immunized infants with pertussis. This suggests that the ACV has provided better protection against severe pertussis requiring hospitalization than the WCV.


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