A Preliminary Study to Evaluate the Immune Response to a Booster Dose of the Adult Tetanus-Diphtheria Vaccine (Td) Available in Iran

Despite the availability of tetanus-diphtheria (TD) vaccines in Iran, the seroconversion rate of these products as a booster dose is unknown. This study evaluates the seroconversion rate of the Iranian Td vaccine in adults who have not been vaccinated in the past decade. In this study, 20 adult volunteers aged 18 to 60 who had not received the Td vaccine in the past decade received a booster dose of the Iranian Td vaccine. Twenty-eight days after vaccination, the seroconversion rate was evaluated using the ELISA method. Vaccine adverse events were monitored at three time points after vaccination. Seroconversion rates with the Iranian Td vaccine boosters were 75% and 90%, respectively, based on a 4-fold increase in anti-tetanus toxoid antibody titers and a 2- and 4-fold combination. Significant associations were found between the demographic data, specifically female gender and age 43 years and older, with seroconversion rates. Injection-site pain was the most common adverse reaction, with a frequency of 35%. No adverse events were reported between one week and one month after vaccination. Results showed that a booster dose of the Iranian Td vaccine produced a protective titer (> 0.1 IU/mL) and a long-term protective titer (> 1.0 IU/mL) in 100% of participants. The seroconversion rate of the Iranian Td vaccine was comparable to other common tetanus vaccines, including Tenivac®, Adacel®, Infanrix®, Tetavax®, and Vacteta®. The proportion of suitable candidates for plasma donation, based on minimum (2 IU/mL) and maximum (10 IU/mL) anti-tetanus toxoid antibody titers, was 100% and 45%, respectively.