DPT vaccine

DPT (also DTP and DTwP) refers to a class of combo 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 (also DTPa and TDaP) refers to similar combination vaccines in which the pertussis component is acellular.

Also available is the DT or TD vaccine, which lacks the pertussis component.

In the Netherlands, the acronym DTP refers to a combination vaccine against diphtheria, tetanus, and poliomyelitis. There, 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 vaccines are used that adjust the relative concentrations of their components.

Combination vaccines with whole cell pertussis

While pertussis was thought to have been eradicated entirely from the United States, in recent years the disease has made a comeback and resulted in fatalities.^[1] At the same time, many parents have declined to vaccinate their children against the disease for fear of side effects;^[1] however, most side effects of the vaccination are moderate and severe problems closely following DPT immunization happen very rarely. These include a serious allergic reaction, prolonged seizures, a decrease in consciousness, lasting brain disease, or death. A study published in the journal Pediatrics in 2009 concluded that the largest risk among unvaccinated children is the disease the vaccination is designed to protect against.^[1]

British research in the 1980s into whole-cell DTP,^[2] which is now rarely available in developed countries, suggested that such severe neurologic events occur after approximately 1 in 140,000 doses of the DPT vaccine (0.0007%). Most of the reactions to whole-cell DPT injection are thought to be from the pertussis component.

In 1994, the Institute of Medicine of the US National Academy of Sciences published a report stating that if the first symptoms of neurological damage occurred within the first seven days following vaccination with whole-cell pertussis vaccine, the evidence was compatible with the possibility that it could be the cause of permanent brain damage in otherwise apparently healthy children. It continued by stating:

This serious acute neurologic response to whole-cell DPT is a rare event. The estimated excess risk ranged from 0 to 10.5 per million immunizations (IOM, 1991). The committee stresses that this is not the strongest statement regarding causality; the evidence does not "establish" or "prove" a causal relation....

The evidence remains insufficient to indicate the presence or absence of a causal relation between DPT and chronic nervous system dysfunction under any other circumstances. That is, because the NCES is the only systematic study of chronic nervous system dysfunctions after DPT, the committee can only comment on the causal relation between DPT and those chronic nervous system dysfunctions under the conditions studied by the NCES. In particular, the chronic dysfunctions associated with DPT followed a serious acute neurologic illness that occurred in children within 7 days after receiving DPT.^[3]

Moderate reactions to DTP vaccines occur in 0.1% to 1.0% of children and include ongoing crying (for three hours or more), a high fever (up to 40 °C / 105 °F), and an unusual, high-pitched crying.

Since 2002, whole-cell pertussis vaccines are no longer used in the US.

Combination vaccines with acellular pertussis

DTaP

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. Most of the developed world has switched to DTaP, but developing countries continue to use DTP. Both DTP and DTaP appear to be equally efficacious in generating immunity.

The acellular vaccine is safer in that it causes substantially fewer side-effects (estimated at 90% fewer), which commonly include local pain and redness, and/or fever.

DTaP was introduced in the US in 1991.

Tdap

Tdap, sometimes known as dTap,^[4] 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 ages 10 to 19.

The U.S.'s Advisory Committee on Immunization Practices (ACIP) and Canada's National Advisory Committee on Immunization (NACI) both recommended adolescents and adults receive Tdap in place of their next Td booster (recommended to be given every 10 years).^{[5] [6] [7][8]} Tdap can be used as prophylaxis for tetanus 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 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.

Thimerosal (Thiomersal)

Thimerosal is a preservative sometimes used with certain vaccines. Out of the eight manufactured DPT vaccines, only three ever contained thimerosal. Currently, seven out of the eight DPT vaccines on the market do not use thimerosal, and the product that does (Tripedia) contains trace levels, less than 0.3 micrograms per dose.^[9] While concerns about the safety of the compound exist, the World Health Organization has concluded that there is no evidence of toxicity from thiomersal in vaccines.^[10]

Medication errors

In August 2006, the non-profit patient safety organization Institute for Safe Medication Practices described medication errors from the confusion between the two different formulations.^[11]

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.

References