Natasha S Crowcroft1,2,3, Kevin L Schwartz2,3,4,5, Rachel D Savage3,6, Cynthia Chen4, Caitlin Johnson4, Ye Li2,4, Alex Marchand-Austin4, Shelly Bolotin1,2,4, Shelley L Deeks2,4, Frances B Jamieson1,4, Steven J Drews7,8, Margaret L Russell9, Lawrence W Svenson10,11,12, Kimberley Simmonds9,10,12, Christiaan H Righolt13, Christopher Bell9, Salaheddin M Mahmud13, Jeffrey C Kwong2,3,4,14. 1. Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada. 2. Centre for Vaccine Preventable Diseases, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada. 3. Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada. 4. Public Health Ontario, Toronto, Ontario, Canada. 5. St Joseph's Health Centre, Toronto, Ontario, Canada. 6. Women's College Research Institute, Women's College Hospital, Toronto, Ontario, Canada. 7. Medical Microbiology, Canadian Blood Service, Edmonton, Alberta, Canada. 8. Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta, Canada. 9. Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada. 10. Alberta Health, Edmonton, Alberta, Canada. 11. Division of Preventive Medicine, University of Alberta, Edmonton, Alberta, Canada. 12. School of Public Health, University of Alberta, Edmonton, Alberta, Canada. 13. Vaccine and Drug Evaluation Centre, Department of Community Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada. 14. Department of Family and Community Medicine, University of Toronto, Toronto, Ontario, Canada.
Abstract
BACKGROUND: Vaccine effectiveness (VE) studies provide essential evidence on waning vaccine-derived immunity, a major threat to pertussis control. We evaluated how study design affects estimates by comparing 2 case-control studies conducted in Ontario, Canada. METHODS: We compared results from a test-negative design (TND) with a frequency-matched design (FMD) case-control study using pertussis cases from 2005-2015. In the first study, we identified test-negative controls from the public health laboratory that diagnosed cases and, in the second, randomly selected controls from patients attending the same physicians that reported cases, frequency matched on age and year. We compared characteristics of cases and controls using standardized differences. RESULTS: In both designs, VE estimates for the early years postimmunization were consistent with clinical trials (TND, 84%; FMD, 89% at 1-3 years postvaccination) but diverged as time since last vaccination increased (TND, 41%; FMD, 74% by 8 years postvaccination). Overall, we observed lower VE and faster waning in the TND than the FMD. In the TND but not FMD, controls differed from cases in important confounders, being younger, having more comorbidities, and higher healthcare use. Differences between the controls of each design were greater than differences between cases. TND controls were more likely to be unvaccinated or incompletely vaccinated than FMD controls (P < .001). CONCLUSIONS: The FMD adjusted better for healthcare-seeking behavior than the TND. Duration of protection from pertussis vaccines is unclear because estimates vary by study design. Caution should be exercised by experts, researchers, and decision makers when evaluating evidence on optimal timing of boosters. Her Majesty the Queen in Right of Canada, as represented by the Public Health Ontario, 2020.
BACKGROUND: Vaccine effectiveness (VE) studies provide essential evidence on waning vaccine-derived immunity, a major threat to pertussis control. We evaluated how study design affects estimates by comparing 2 case-control studies conducted in Ontario, Canada. METHODS: We compared results from a test-negative design (TND) with a frequency-matched design (FMD) case-control study using pertussis cases from 2005-2015. In the first study, we identified test-negative controls from the public health laboratory that diagnosed cases and, in the second, randomly selected controls from patients attending the same physicians that reported cases, frequency matched on age and year. We compared characteristics of cases and controls using standardized differences. RESULTS: In both designs, VE estimates for the early years postimmunization were consistent with clinical trials (TND, 84%; FMD, 89% at 1-3 years postvaccination) but diverged as time since last vaccination increased (TND, 41%; FMD, 74% by 8 years postvaccination). Overall, we observed lower VE and faster waning in the TND than the FMD. In the TND but not FMD, controls differed from cases in important confounders, being younger, having more comorbidities, and higher healthcare use. Differences between the controls of each design were greater than differences between cases. TND controls were more likely to be unvaccinated or incompletely vaccinated than FMD controls (P < .001). CONCLUSIONS: The FMD adjusted better for healthcare-seeking behavior than the TND. Duration of protection from pertussis vaccines is unclear because estimates vary by study design. Caution should be exercised by experts, researchers, and decision makers when evaluating evidence on optimal timing of boosters. Her Majesty the Queen in Right of Canada, as represented by the Public Health Ontario, 2020.
Authors: Jeffrey C Kwong; Sarah A Buchan; Hannah Chung; Michael A Campitelli; Kevin L Schwartz; Natasha S Crowcroft; Michael L Jackson; Timothy Karnauchow; Kevin Katz; Allison J McGeer; J Dayre McNally; David C Richardson; Susan E Richardson; Laura C Rosella; Andrew Simor; Marek Smieja; George Zahariadis; Aaron Campigotto; Jonathan B Gubbay Journal: Vaccine Date: 2019-06-17 Impact factor: 3.641
Authors: Sarah L Sheridan; Katie Frith; Thomas L Snelling; Keith Grimwood; Peter B McIntyre; Stephen B Lambert Journal: Expert Rev Vaccines Date: 2014-08-05 Impact factor: 5.217
Authors: Evan W Orenstein; Gaston De Serres; Michael J Haber; David K Shay; Carolyn B Bridges; Paul Gargiullo; Walter A Orenstein Journal: Int J Epidemiol Date: 2007-04-02 Impact factor: 7.196