Tetanus antibodies measured by the toxin binding inhibition test (ToBI) in mothers and children in the Neonatal Tetanus Program in Vietnam

Abstract

The immunoresponse to vaccination in the Neonatal Tetanus Program (NNT) for pregnant women was studied in Vietnam using the Toxin Binding Inhibition Test (ToBI). The vaccination schedule consisted of two primary doses of adsorbed tetanus toxoid (TT) vaccine given with a one month interval. The seroconversion rate in the women was 98%. Two and a half months after birth, 63% of the children born from these women had tetanus antibody values higher than 0.01 IU/ml. Four women who had anti-tetanus titres < 0.01 IU/ml at delivery, despite two doses of primary vaccination, received a third booster with vaccine one year after the first injection. Their antibody levels were well above 0.01 IU/ml one month after this additional booster, suggesting that (when economically feasible) a third TT injection could be considered into the NNT to confer optimal anti-tetanus antibody levels in women for subsequent pregnancies. This study confirmed the effectiveness of the TT vaccines investigated and indicates their potential to replace, in immunosurveillance studies under field conditions, the in vivo mouse neutralisation test by in vitro alternative methods such as the ToBI test.