Immunologic response to tetanus toxoid in the elderly: One-year follow- up

Study objective: To determine whether elderly patients documented to have nonprotective titers of anti-tetanus antibodies (ATA) are able to achieve and maintain protective ATA titers for at least 1 year after tetanus immunization. Methods: Thirty-five outpatients aged 65 or older with documented inadequate ATA titers were given 1 tetanus immunization. Repeat titers were obtained 2 months and 12 months after immunization. Titers were measured with an enzyme-linked immunoassay kit (Bindazyme kit). ATA titers in excess of .17 IU were considered protective. The study was conducted at a large urban geriatric center. Results: The mean age of participants was 78.7 years; 86% (24/28) were women. Repeat ATA titers were obtained an average of 122 days and 493 days after immunization. The mean preimmunization ATA titer was .1 IU, (range .04 to .16 IU). After immunization, the 2-month ATA titer rose a mean of .61 (95% confidence interval [Cl] .35 to .87) IU, with 86% (30/35) achieving protective titers. After 1 year only 28 of 35 patients were available for follow-up. Protective titers had been present in all 7 patients lost to follow-up. After 1 year, 82% (23/28) patients had protective titers. The mean ATA titer for the 28 patients was .54 (95% Cl -.78 to 1.86) IU, a significant increase from preimmunization levels (P=.002). However, ATA titers changed -.18 (95% Cl -.98 to .62) IU between 2 months and 1 year (P=.02). There was no correlation between gender, country of birth, and medical history with development or maintenance of protective titers. Conclusion: Administration of 1 tetanus toxoid affords protective immunization to a large portion of the elderly population after 1 year.