<P> In the latter 20th century, vaccinations helped to reduce the incidence of childhood pertussis in the United States . Despite this, reported instances of the disease increased twenty-fold in the early 21st century, resulting in numerous fatalities . Over this time, many parents declined to vaccinate their children against pertussis for fear of side effects . In 2009, The journal Pediatrics concluded the largest risk among unvaccinated children was not the contraction of side effects, but rather the disease that the vaccination aims to protect against . </P> <P> DTP was licensed in 1949 . </P> <P> DTaP and Tdap are both combined vaccines against diphtheria, tetanus, and pertussis . The difference is in the dosage, with the upper case letters meaning higher quantity . The names are easy to confuse, and the Institute for Safe Medication Practices reports hundreds of cases of accidental mix - ups . </P> <P> DTaP (also DTPa and TDaP) is a combined vaccine against diphtheria, tetanus, and pertussis, in which the pertussis component is acellular . This is in contrast to whole - cell, inactivated DTP (aka DTwP). The acellular vaccine uses selected antigens of the pertussis pathogen to induce immunity . Because it uses fewer antigens than the whole cell vaccines, it is considered safer, but it is also more expensive . Recent research suggests that the DTP vaccine is more effective than DTaP in conferring immunity; this is because DTaP's narrower antigen base is less effective against current pathogen strains . </P>

What's the difference between dtp and dtap