DTaP combines vaccines against diphtheria, tetanus and pertussis. It is currently given as a series of five doses, recommended at 2 months, 4 months, 6 months and 12 to 18 months, with a booster dose between 4 and 6 years.
Diphtheria generally causes a throat infection, although it also can lead to problems in other parts of the body. The mucous membranes of the throat swell and then become thin and fragile. The infection can cause blockage of the airway, or it can spread into the bloodstream and then to the heart, nerves or brain. Diphtheria is not common in the United States, but pockets of outbreak do occur. It is far more common in developing countries. It is considered important to have a diphtheria vaccine prior to any international travel.
Tetanus is well known. If you step on a rusty nail or get a dirty cut, the bacteria that carry the tetanus toxin can enter the skin and multiply. The wound must be deep for these bacteria to grow, because they can survive only in an environment without any oxygen (called anaerobic). The bacteria release a nerve toxin that causes muscle spasms sometimes so severe that the muscles become completely rigid. Lockjaw (also called trismus) is a classic symptom of tetanus. The breathing muscles can become spastic as well, a potentially life-threatening complication.
Pertussis is more commonly known as whooping cough. In older children, teens, and adults, pertussis causes a persistent (or staccato) cough that goes on for so long that the infected person must gasp and inhale deeply to catch his breath. This is the “whoop” of whooping cough. In infants, especially those under six months, pertussis can cause regular breathing to stop suddenly (called apnea) even before a cough is heard. In some studies, it is estimated that 25 to 30 percent of adults who have been coughing for more than three weeks carry pertussis. One reason pertussis is so prevalent is that the immunity against the infection disappears several years after the last dose of the vaccine. Until 2005, teens and adults had not routinely been vaccinated against pertussis. Instead, they received a booster diphtheria-tetanus vaccine without pertussis. Therefore, many adolescents and almost all adults serve as reservoirs for this bacteria. Since 2005, however, a new tetanus booster vaccine that includes protection against pertussis has been available for adults up to age 65. Although older children and adults can get morbidly sick with pertussis, this is quite rare. Infants are at greatest risk when they are infected.
The DTaP formulation of the vaccine has been widely available since 1996. Before that, DPT was used instead. DPT had whole-cell pertussis, not acellular pertussis. The old DPT form was fraught with side effects. It often caused fevers up to 104° to 105°F, which in turn led to febrile seizures in some children. DPT was also responsible for several infant deaths due to shock. When the formulation of pertussis was changed, the side effects of the vaccine became significantly less severe. DPT is no longer used in the United States.
The most common adverse reactions reported with DTaP include pain or soreness at the injection site (5 in 100 children), low-grade fever (5 in 100), fussiness (30 in 100), and swelling at or around the injection site (8 in 100). Only 1 in 3,000 children experiences a high fever. These symptoms resolve in one to three days. Other adverse reactions include continuous screaming or crying for more than three hours (1 in 2,000), seizures (6 in 10,000), and allergy to one of the components.
Many people ask whether the components of DTaP are available separately. Although some countries do carry pertussis vaccine on its own, it is neither manufactured nor available in the United States this way. For now, the only way to be vaccinated against pertussis is to have the combined DTaP vaccine. Tetanus vaccine is available either alone (T) or with diphtheria (TD), but neither T nor TD is recommended for children under seven. In addition, both of these forms tend to contain significant amounts of thimerosal.