Routine immunization of infants and children with acellular Pertussis (aP) vaccine is recommended at 2, 4, 6 and 15-18 months of age with a booster dose at 4-6 years of age. It is given in a combination with Diphtheria and Tetanus vaccines called DTaP. The effectiveness of the vaccine in children who have received at least 3 doses is estimated to be 80%; and protection is even greater against severe disease. Protection will begin to diminish after about 3 years. Persons who experience pertussis after immunization usually have a milder case. DTaP vaccine is currently recommended for children 2 months through 6 years of age.