Painless DTP vaccine are subunit type of vaccines containing only a part of Pertussis causing bacteria and not the whole of it. They are actually DTaP vaccines but known as painless as they do not cause pain and fever. Recent research has shown that DTaP fails to prevent transmission and spread of Pertussis among people as it does not prevent Pertussis from entering and living inside the airways of vaccinated persons. So, the vaccinated persons are themselves immune, but can still spread the disease to non vaccinated persons or ones with weak immunity. Also DTaP provides lesser immunity than DTwP vaccine. This is the reason, DTaP vaccine /combinations should preferably be avoided for the primary series of infant immunization. There were recent news of Pertussis outbreaks in USA where DTaP vaccines are more common.
According to new IAP recommendations, DTaP vaccines should no longer be given to infants now. However in cases of severe allergies to DTwP vaccines, DTaP vaccine should be given. If baby is given primary doses of painless vaccines already, no need to repeat the doses. Two booster doses below 7 years of age, should essentially be of DTwP vaccines to provide longer and effective immunity in those cases.