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Inclusion Criteria:

Cases were included if they met the following inclusion criteria:

* Reported pertussis disease in the referenced EIP surveillance database
* Age greater than 2 days and younger than two months of age
* Resided in the catchment area on date of onset of their cough
* Born in a hospital in their state of residence
* ≥ 37 weeks of gestation at birth
* Not adopted, in foster care or living in a residential care facility
* Completed maternal interview
* Completed infant and maternal information

Controls were included if they met the following inclusion criteria:

* Age greater than 2 days and younger than 2 months of age on date of cough onset for the corresponding case infant
* Resided in the catchment area on date of cough onset for the corresponding case infant
* Born in a hospital in their state of residence
* ≥ 37 weeks of gestation at birth
* Not adopted, in foster care or living in a residential care facility
* Maternal interview completed
* Infant and maternal information complete

Exclusion Criteria:

Cases were excluded if they met any of the following exclusion criteria:

* Vaccination status of the mother unknown
* Infants whose mothers were vaccinated with Boostrix or an unknown vaccine brand

Controls were excluded if they met any of the following exclusion criteria:

* Vaccination status of the mother unknown
* A pertussis diagnosis prior to the cough onset date of the corresponding case infant
* Controls that were matched to Boostrix or an unknown brand cases

• Lyon, France