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Table 2 ER Visits and Admissions in the first 72 h following vaccination versus days 9 to 18 for the time period when whole cell pertussis vaccine was used compared to the time period when acellular pertussis vaccine was used [23]

From: The use of relative incidence ratios in self-controlled case series studies: an overview

 

Risk events (first 72 h)

Control events (Day 9–18)

Relative incidence

95 % CI

Relative incidence ratio

95 % CI

P-valuea

Apr 94–Mar96 (whole-cell)

1323

3663

1.08

1.02–1.15

1.82

1.64–2.01

P < 0.0001

Apr98–Mar00 (acellular)

697

3508

0.60

0.55–0.65

1 (ref)

-

-

  1. ap-value for interaction of time period (whole cell or acellular periods) with risk