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DPT (also DTP and DTwP) refers to a class of combination vaccines against three infectious diseases in humans: diphtheria, pertussis (whooping cough), and tetanus. The vaccine components include diphtheria and tetanus toxoids and killed whole cells of the organism that causes pertussis (wP).
DTaP and Tdap refer to similar combination vaccines in which the component with lower case 'a' is acellular.
Also available is the DT or TD vaccine, which lacks the pertussis component. The Tdap vaccine is currently recommended by the CDC and covers tetanus, diphtheria and pertussis (CDC Vaccines, 2013).
In the Netherlands and in France, the abbreviation DTP refers to a combination vaccine against diphtheria, tetanus, and poliomyelitis. In the Netherlands, pertussis is known as kinkhoest and DKTP refers to a combination vaccine against diphtheria, pertussis/kinkhoest, tetanus, and polio.
The usual course of childhood immunization is five doses between 2 months and 15 years. For adults, separate combination (booster) vaccines are used that adjust the relative concentrations of their components.
While vaccinations helped eradicate pertussis from the United States in the latter half of the 20th century, in recent years the disease resurfaced and resulted in fatalities. Many parents decline to vaccinate their children against the disease for fear of side effects. In 2009, Pediatrics concluded the largest risk among unvaccinated children is the disease the vaccination is designed to protect against.
DTP was licensed in 1949.
Combination vaccines with acellular pertussis
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.
DTaP (also DTPa and TDaP) is a combined vaccine against diphtheria, tetanus, and pertussis, in which the component with lower case 'a' 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.
The acellular vaccine is safer to administer in that it causes substantially fewer side-effects (estimated at 90% fewer), which commonly include local pain and redness, or fever.
DTaP was developed in Japan in 1981.
Recent research has shown that while DTaP does confer immunity, it does not prevent transmission because it does not prevent Pertussis from colonizing the airways of vaccinated individuals. Thus people who have received DTaP can infect unvaccinated or immunocompromised people.  Other recent research has shown that DTaP confers less immunity that whole cell DTP (aka DTwP). 
Tdap, sometimes known as dTap, is the acronym for the collective vaccines preventing tetanus, diphtheria, and pertussis in adolescents and adults that were licensed in the United States in spring of 2005. These vaccines differ from the childhood DTaP vaccines (brand name Daptacel) in their indication. As indicated by the lower case "d" and "p", the concentration of diphtheria and pertussis toxoids has been reduced in these "adult" formulations to prevent adverse effects, while the "a" in "ap" indicates that the pertussis toxoids are acellular. Two Tdap vaccines are available in the U.S. Adacel, manufactured by Sanofi Pasteur, is licensed for use in adults ages 11 to 64. Boostrix, manufactured by GlaxoSmithKline, is licensed for use in adolescents and adults ages 10 to 64. The U.S.'s Advisory Committee on Immunization Practices (ACIP) has recommended its use in adults of all ages, including those age 65 and above. After the 2010 passage of Assembly Bill 354, the State of California requires all students entering grades 7-12 provide proof of Tdap vaccination as a condition of enrollment in both public and private schools.
The U.S.'s Advisory Committee on Immunization Practices (ACIP) and Canada's National Advisory Committee on Immunization (NACI) recommended that both adolescents and adults receive Tdap in place of their next Td booster (recommended to be given every 10 years). Tdap can be used as prophylaxis for tetanus in wound management. Five years between doses of Td or doses of Td and Tdap is the current standard of care; frequent exposure to tetanus toxoid can cause local reactions. People who will be in contact with young infants are encouraged to get Tdap even if it has been less than 5 years since Td or TT to reduce the risk of infants being exposed to pertussis. The ACIP statement on Tdap use in adolescents encourages 5 years between Td and Tdap to reduce this[specify] risk; however, both suggest that shorter intervals may be appropriate in some circumstances, such as for protection in pertussis outbreaks. NACI suggests intervals shorter than 5 years can be used for catch-up programs and other instances where programmatic concerns make 5-year intervals difficult.
Thiomersal (INN), commonly known in the US as thimerosal,is a preservative sometimes used with certain vaccines. Out of the eight manufactured DPT vaccines, only three ever contained thiomersal. Currently, seven out of the eight DPT vaccines on the market do not use thiomersal, and the product that does (Tripedia) contains trace levels, less than 0.3 micrograms per dose. The World Health Organization has concluded that there is no evidence of toxicity from thiomersal in vaccines.
There were several mix-ups between DAPTACEL and ADACEL. Daptacel is for active immunization in infants and children 6 weeks to 6 years old. Adacel is indicated for active booster immunization as a single dose in persons 11 to 64 years old and is the first vaccine approved as a pertussis booster for adults. The component antigens in Adacel and Daptacel are the same, but the relative amounts are much greater with the infant vaccination. As such, these are easy to confuse.
In one clinic, 13 adults were vaccinated with Daptacel in error. At another clinic, seven adults received Daptacel instead of Adacel. None of the patients appeared to have experienced any unusual vaccine reactions despite the fact that the pediatric formulation contains greater amounts of the detoxified pertussis toxin and diphtheria toxoid. The similarities of the brand names, generic designations, and vaccine abbreviations (Tdap and DTaP) were felt to have contributed to the confusion.
The World Health Organization recommends a pentavalent vaccine, combining the DTP vaccine with vaccines against Haemophilus influenzae type B and hepatitis B. There is not yet sufficient evidence on how effective this pentavalent vaccine is in relation to the individual vaccines.
Guidelines on prenatal care in the United States state that, if an urgent need for tetanus protection occurs during pregnancy, Td vaccine should be administered. If no urgent need arises and the woman has previously received tetanus vaccine, Td vaccination should be delayed until the postpartum period. All postpartum women who have not received Td or Tdap vaccine in the last two years are recommended to receive Tdap prior to discharge after delivery. It is recommended for pregnant women who have never received tetanus vaccine (i.e., have never received DTP, DTaP or DT as child or Td or TT as adult) to receive a series of three Td vaccinations starting during pregnancy to ensure protection against maternal and neonatal tetanus. In such cases, administration of Tdap is recommended after 20 weeks' gestation, and in earlier pregnancy a single dose of Tdap can be substituted for one dose of Td, and then the series completed with Td. The United States Center for Disease Control (CDC) Advisory Committee on Immunization Practices (ACIP) voted to recommend that health-care personnel should administer a dose of Tdap during each pregnancy at 27 through 36 weeks gestation irrespective of the patient's prior history of receiving Tdap....
- "Is Vaccine Refusal Worth The Risk?". NPR. 2009-05-26. Retrieved 2009-06-19.
- The difference between Tdap and DTaP; dabigatran versus warfarin - JAAPA
- DTaP-Tdap mix-ups now affecting hundreds of patients
- Higgs, Higgins, Ross and Mills 2012 'Immunity to the respiratory pathogen Bordatella pertussis' Mucosal Immunol 5(5):485-500
- "Hong Kong Childhood Immunisation Programme". 2013.
- "Updated recommendations for use of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) vaccine from the Advisory Committee on Immunization Practices, 2010". MMWR Morb. Mortal. Wkly. Rep. 60 (1): 13–5. January 2011. PMID 21228763.
- Staff Reports (May 15, 2012). "No shot, no school reminder issued to parents". Freedom Communications. Retrieved 2012-06-09.
- California State Legislature (September 29, 2010). "AB 354 Assembly Bill". Legislative Counsel of California. Retrieved 2012-06-09.
- Broder KR, Cortese MM, Iskander JK, et al. (Mar 2006). "Preventing tetanus, diphtheria, and pertussis among adolescents: use of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccines recommendations of the Advisory Committee on Immunization Practices (ACIP)". MMWR Recomm Rep 55 (RR–3): 1–34. PMID 16557217., page 18.
- "ACIP Votes to Recommend Use of Combined Tetanus, Diphtheria and Pertussis (Tdap) Vaccine for Adults" (PDF).
- "Interval Between Administration of Vaccines Against Diphtheria, Tetanus, and Pertussis".
- Kretsinger K, Broder KR, Cortese MM, et al. (December 2006). "Preventing tetanus, diphtheria, and pertussis among adults: use of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccine recommendations of the Advisory Committee on Immunization Practices (ACIP) and recommendation of ACIP, supported by the Healthcare Infection Control Practices Advisory Committee (HICPAC), for use of Tdap among health-care personnel". MMWR Recomm Rep 55 (RR–17): 1–37. PMID 17167397.
- United States Food and Drug Administration. "Thiomersal in Vaccines".
- Global Advisory Committee on Vaccine Safety (2006-07-14). "Thiomersal and vaccines". World Health Organization. Retrieved 2007-11-20.
- "Adacel (Tdap) and Daptacel (DTaP) confusion". ISMP Medication Safety Alert!. Institute for Safe Medication Practices. August 24, 2006.
- Bar-On ES, Goldberg E, Hellmann S, Leibovici L (2012). "Combined DTP-HBV-HIB vaccine versus separately administered DTP-HBV and HIB vaccines for primary prevention of diphtheria, tetanus, pertussis, hepatitis B and Haemophilus influenzae B (HIB)". Cochrane Database Syst Rev (4): CD005530. doi:10.1002/14651858.CD005530.pub3. PMID 22513932.
- Health Care Guideline: Routine Prenatal Care. Fourteenth Edition. By the Institute for Clinical Systems Improvement. July 2010.
- Updated Recommendations for Use of Tetanus Toxoid, Reduced Diphtheria Toxoid and Acellular Pertussis Vaccine (Tdap) in Pregnant Women and Persons Who Have or Anticipate Having Close Contact with an Infant Aged <12 Months, 2011 - section "Safety of Tdap in Pregnant Women". By the Advisory Committee on Immunization Practices (ACIP), at Centers for Disease Control and Prevention.
- Tdap Vaccine: What You Need to Know, vaccine information statement (5/9/2013 release)
- Td or Tdap Vaccine: What You Need to Know, vaccine information statement (5/17/2007 release)