Diphtheria, Tetanus and A Cellular Pertussis (DTaP) Immunization

DIPHTHERIA, TETANUS AND A CELLULAR PERTUSSIS (DTAP) IMMUNIZATION

Immunization against these three unrelated diseases is considered together because the vaccines are non-living and are often co-administered as a triple vaccine as part of the childhood vaccination programme.

a)  Diphtheria

This is an acute, non-invasive infectious disease associated with the upper respiratory tract . The incubation period is 2-5 days although the disease remains communicable for up to 4 weeks. A low molecular weight toxin is produced which affects the myocardium, nervous and adrenal tissues. Death results in 3-5% of infected children. Diphtheria immunization stimulates the production of an antitoxin which protects against the disease but not against infection/colonization of the respiratory tract. The immunogen is a toxoid, prepared by formaldehyde treatment of the purified toxin and administered while adsorbed to an adjuvant, usually aluminium phosphate or aluminium hydroxide. The primary course of diphtheria prophylaxis consists of three doses starting at 2 months of age and separated by an interval of at least 1 month. The immune status of adults may be determined by administration of Schick test toxin, which is essentially a diluted form of the vaccine.

b)  Tetanus

Tetanus results from the production of a toxin by germinating spores and vegetative cells of Clostridium tetani that can potentially infect deep wounds. The organism, which may be introduced into the wound, grows anaerobically at such sites. The toxin is adsorbed into nerve cells and has a profound effect on nerve synapses resulting in spastic paralysis in affected individuals. Mortality rates are highest in individuals over 60 years of age and the unvaccinated. Tetanus immunization employs a toxoid and protects by stimulating the production of antitoxin. This antitoxin will neutralize the toxin as the organisms release it and before it can be adsorbed into nerves. As the toxin is produced only slowly after infection, the vaccine, which acts rapidly, may be used prophylactically in non-immunized individuals who have recently suffered a high-risk injury. The toxoid, as with diphtheria toxoid, is formed by reaction with formaldehyde and is adsorbed onto an inorganic adjuvant. The primary course of tetanus vaccination consists of three doses starting at 2 months of age and is separated by an interval of at least 1 month.

c)  Pertussis (Whooping Cough)

Whooping cough is caused by the non-invasive respiratory pathogen Bordetella pertussis. This disease may be complicated by broncho-pneumonia, or by repeated posttussis vomiting leading to weight loss and to cerebral hypoxia associated with a risk of brain damage. Until the mid 1970s the mortality from whooping cough was about 1 per 1000 notified cases, with a higher rate for infants under 1 year of age. A full course of vaccine now consists of highly purified selected components of the Bordetella pertussis organism (i.e. acellular pertussis) which are treated with formaldehyde or glutaraldehyde and absorbed on to aluminium phosphate or aluminium hydroxide adjuvants. This vaccine gives considerably lower incidence of local and systemic reactions in comparison to the whole-cell pertussis vaccine that preceded it and gives comparable protection (> 80%). The primary course of pertussis prophylaxis consists of three doses starting at 2 months of age and separated by an interval of at least 1 month.

d)  DTaP Vaccine Combinations And Administration

The primary course of DTaP protection consists of three doses of a combined vaccine, each dose separated by at least 1 month and commencing not earlier than 2 months of age. In such combinations, the pertussis component of the vaccine acts as an additional adjuvant for the toxoid elements. Tetanus and diphtheria vaccines are also available in a combined tetanus/diphtheria/inactivated polio vaccine (Td/IPV) vaccine.

The primary course of pertussis vaccination is considered sufficient to confer lifelong protection, especially as the mortality associated with disease declines markedly after infancy. The risks associated with tetanus and diphtheria infection however persist throughout life. The Td/IPV vaccination is therefore repeated before school entry, at 4-5 years of age, and once again at puberty.