The DTaP vaccine series is recommended to help protect against diphtheria, tetanus, and pertussis in infants and young children.  Individuals susceptible to these vaccine-preventable diseases can develop life-threatening complications and even death.  Since the development of universal vaccines in the 1940s, the number of reported cases from diphtheria, tetanus, and pertussis declined in the United States. 

Tetanus is an infectious disease caused by neurotoxins produced by the gram-positive bacillus, Clostridium tetani.  The heat resistant spores of the bacteria enter the body at mucous membranes or a breach in the skin.  Toxins are formed, including a highly potent toxin called tetanospasmin. This toxin interferes with the release of neurotransmitters in the central nervous system leading to unopposed muscle contraction and spasm. There is no person to person transmission of C. tetani.[1][2]

Moreover, diphtheria results from infection with toxin-producing strains of Corynebacterium diphtheriae, gram-positive bacillus. The disease is transmissible from person to person by droplets or close contact. The bacteria can multiply and produce the diphtheria toxin in the nasopharynx region, mucous membranes, or skin lesions. Early symptoms can include malaise, sore throat, and low-grade fever.  A classic feature of respiratory diphtheria is a gray-colored pseudo-membrane that firmly adheres to the mucosal lining of nasopharynx, tonsils, or larynx. This pseudo-membrane can extend further into the nasal cavity or larynx, obstructing the airways. Cardiac and neurological complications can occur once the toxin reaches the bloodstream. Respiratory droplets or close contact can transmit diphtheria.[1][3]

Pertussis is a respiratory disease, also known as whooping cough, caused by the gram-negative bacillus, Bordetella pertussis. The disease characteristically has three stages: catarrhal, paroxysmal, and convalescent. The catarrhal stage includes symptoms of coryza, mild cough, and low-grade fever. Around one to two weeks, the infected person enters the paroxysmal stage with symptoms of spasmodic coughing, posttussive vomiting, and inspiratory whoop. Symptoms slowly improve in the convalescent stage but can last for weeks to months. B. pertussis is transmittable through aerosolized droplets generated by cough or sneezing. People are most infectious at the catarrhal stage or beginning of the paroxysmal stage.[1][4]

The DTaP vaccine consists of diphtheria and tetanus toxoids (inactivated toxins) and acellular pertussis antigens. The tetanus component of the vaccine is about 5 to 10 levels of flocculation (Lf) units of manufactured tetanus toxoid. The diphtheria component is a manufactured diphtheria toxoid of about 15 to 25 Lf units. The acellular pertussis component of a DTaP vaccine consists of manufactured pertussis antigens called pertussis toxin, filamentous haemagglutinin, pertactin, and fimbriae type 2 and 3.[1]

 The vaccine produces an active immune response of the body by developing antibodies and antitoxins against the toxoids and acellular pertussis antigens. There are two single DTaP vaccines available in the United States and approved by the FDA.

The CDC’s Advisory Committee on Immunization Practices (ACIP) recommends administering the DTaP five-dose vaccine series for children six weeks continuing through to six years of age.[5] Routine dose recommendations are for the following ages:

• Two months: minimum age of six weeks
• Four months: the second dose should be given at least four weeks after the first
• Six months: the third dose should be given at least four weeks after the second
• Fifteen through eighteen months: the minimum age for the fourth dose is 12 months and should be given at a minimum of six months after the third dose.  It may be counted as valid if given at least four months after the third dose, and the child was at least 12 months old
• Four through six years: the minimum age for the fifth dose is four years old.  The dose should be given at least six months after the fourth dose.  

The DTaP dose is 0.5 mL and given intramuscularly.  The preferred intramuscular injection site for infants to two years of age is the anterolateral aspect of the thigh. For children at three years of age and older, the preferred site is the deltoid muscle.[1]  DTaP vaccines can also be available in combination with other childhood vaccines.

Children unimmunized or incompletely immunized should receive catch-up immunizations. This process is possible with minimal intervals between doses. 

• Dose 1 to dose 2 - four weeks
• Dose 2 to dose 3 - four weeks
• Dose 3 to dose 4- six months, the minimum age for dose 4 is 12 months
• Dose 4 to dose 5 - six months

The fifth dose is not necessary if the fourth dose was given by at least four years of age and at least four months after the third dose. 

Whole-cell pertussis vaccines, known as DTP vaccines, were commonly associated with local adverse events, including swelling, redness, and pain at the injection site. DTP vaccines were replaced by DTaP vaccines in the 1990s to reduce the number of these common adverse events. Less common adverse events for pertussis vaccines are seizures, hypotonic-hyporesponsive episodes, and prolonged crying.[1][4]

Vaccines with tetanus toxoids can cause brachial neuritis based on case reports and studies reviewed by the World Health Organization and ACIP.  The cases can be severe but are rare, and brachial neuritis is usually self-limited.[1][2]

ACIP has reviewed several studies regarding the simultaneous administration of DTaP with other vaccines. An increased risk may exist for febrile seizures within 24 hours when administering the inactivated influenza vaccine along with the pneumococcal 13-valent conjugate vaccine or the DTaP vaccine. The overall risk for febrile seizures is small, with any combination of vaccines. Therefore, the ACIP recommends a simultaneous administration of these vaccines.[1]

Severe allergic reactions or anaphylaxis after administration of the DTaP vaccine or vaccine component is considered a contraindication. Encephalopathy (coma, a decreased level of consciousness, or prolonged seizures) that occurs within seven days of DTaP administration and with no identifiable cause is also a contraindication.