It is not a case of primary vaccination failure. (caberfeidh.com)
A 1 year booster vaccination is required after primary vaccination, followed by a vaccination every three years.» (catinfo.org)
Pertussis vaccine boosters for close contacts (such as parents, grandparents, nannies, siblings and baby unit nurses), who are the most common sources of transmission to infants, protect those too young to be given primary vaccination with a surrounding «pertussis - free cocoon».38 (who.int)