Earlier this century, diphtheria caused more deaths in Australia than any other infectious disease, but increasing use of diphtheria vaccines since World War II has led to a progressive decline in mortality. Diphtheria has been almost eliminated from Australia, but sporadic cases continue to occur in unimmunised individuals. There is now little possibility of acquiring natural immunity, and no opportunity to boost declining immunity with subclinical infection. A high vaccination rate must therefore be maintained to protect the population from a resurgence of the disease. An increase in the prevalence of infections from toxigenic strains could follow introduction of cases or carriers from overseas, or from local emergence of a virulent strain.
Diphtheria vaccination stimulates the production of antitoxin, which protects against the toxin.
The immunogen is prepared by treating a cell-free purified preparation of toxin with formaldehyde, thereby converting it into the innocuous diphtheria toxoid. The toxoid is usually adsorbed onto an adjuvant, either aluminium phosphate or aluminium hydroxide, to increase its immunogenicity. Antigens from Bordetella pertussis also act as an effective adjuvant. A variety of formulations of diphtheria vaccine is available in Australia. Store at 2-8deg.