Effect on diphtheria immunity of combined tetanus and diphtheria booster vaccination in adults

The effect of a single booster injection of an adult formulation of a combi ned diphtheria-tetanus vaccine (Td) on diphtheria-specific immunity was eva luated. The booster injection, containing 2 IU diphtheria toroid per dose, was given as part of the surgical wound management for adults with open sof t tissue injuries. Diphtheria antitoxin concentrations were determined in s erum samples from 534 patients (199 women and 335 men, aged 18-70 years) us ing an enzyme immunoassay and a tissue culture toxin neutralization assay. Seroimmunity against diphtheria toxin was classified at three levels: susce ptibility, basic protection, and full protection against the toxic manifest ations of the disease. Before vaccination, 27.1% of the subjects were susce ptible to diphtheria, 26.5% had basic protection, and 46.4% were fully prot ected. Six weeks (minimum 25 days, maximum 98 days) after a single booster injection, 89.7% of the subjects achieved full protection against diphtheri a, and only 3.9% had antitoxin levels below the protective level. The media n increase from the prevaccination to postvaccination antitoxin concentrati on was found to be 14-fold (4.4-47; quartiles Q25 to Q75). The change in an titoxin levels after revaccination was higher in older age groups (P < 0.00 1), whereas neither sex (P = 0.86) nor the country of previous immunization with a different national immunization schedule (P = 0.61) had a significa nt influence on the revaccination effect. Systemic adverse reactions were r are, and local reactions of clinical significance were reported in only 1.9 % of subjects.