- Willing to have infant immunized with a pertussis containing vaccine at 2, 4, 6 months and 18 months of age according to EPI (Expanded Programme of Immunization) and receiving (randomized) either acellular pertussis (aP) (study vaccine) or a whole cell pertussis (wP) vaccine. Consent for participation of the child is needed by both married parents or by a single unmarried other.