Pertussis is a vaccine preventable disease caused by Bordetella pertussis. Older children and adolescents with pertussis continue to be a significant source of infection for incompletely vaccinated infants who are in harm for developing severe disease. The primary objective of our study is to estimate the duration of protection elicited by the current vaccination schedule against pertussis in Croatia.

Inclusion Criteria:

• children and adolescents from 6 to 18 years of age treated through Emergency room and/or Day hospital of Pediatric Infectious Diseases Department at UHID;
• appropriate vaccination with pertussis component containing vaccine by date and at the appropriate time, according to Croatian NIP proven by insight in the Vaccination Record Card
• written informed consent obtained from the subject's parent or caregiver, as well as from participants ≥ 16 years old.

Exclusion Criteria:

• children under 6 years
• children and adolescents with acute respiratory symptoms
• children and adolescents with pertussis-like illness within 12 months
• children and adolescents with unknown, uncompleted or irregular vaccination record
• inpatients
• children and adolescents with immunodeficiencies