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

Background: Despite the availability of tetanus-diphtheria (TD) vaccines in Iran, the seroconversion rate of these products as a booster dose is unknown.

Objectives: This study evaluates the seroconversion rate of the Iranian Td vaccine in adults who have not been vaccinated in the past decade.

Methods: 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.

Results: 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.

Conclusions: 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.