Immunologic response to tetanus toxoid in geriatric patients

Study objective: Tetanus antibody levels have been shown to be inadequate in 50% of patients older than 65 years. Although immunization recommendations have been made for this age group, the efficacy of this intervention has not been well documented. We sought to determine the difference in tetanus antibody levels after the administration of one tetanus toxoid immunization to geriatric patients without adequate titers. Methods: Thirty-five patients older than 65 years at a large urban comprehensive care geriatric center who were documented to have inadequate tetanus antibody titers were each given one tetanus toxoid immunization. Repeat titers were obtained at least 2 months after the immunization with the use of enzyme- linked immunosorbent assay (Bindazyme kit; the Binding Site Corporation, Birmingham, England). We considered tetanus antibody levels greater than .17 IU/mL protective. Results: The mean age was 79.4 years; 30 of 35 (86%) were female. Repeat tetanus antibody titers were obtained an average of 123 days (range, 63 to 204 days) after immunization with tetanus toxoid. The mean preimmunization antibody titer was .1 IU/mL (range, .04 to .16 IU/mL). After immunization, antibody titers increased a mean of .61 IU/mL (range, -.01 to 2.23 IU/mL; 95% confidence interval .35 to .87 IU/mL. Thirty of the 35 patients who received a single injection of tetanus toxoid (86%) developed protective titers. We found no relationship between seroconversion and age, sex, or medical history, nor did we find a relationship between antibody level and time elapsed since immunization when repeat titers were obtained. Conclusion: Administration of one tetanus toxoid injection affords protective immunity in many geriatric patients.