Fig. 2
From: The use of relative incidence ratios in self-controlled case series studies: an overview
Emergency room visits and admissions before and after 2-month vaccination for whole cell pertussis combination vaccine (1994–1996) versus acellular pertussis vaccine (1998–2000). Count = number of combined endpoints of emergency room visit, hospitalization and death. Days = number of days before or after vaccination, day 0 being the day of vaccination