Except for one participant in the dTpa-0.3 group, all other
study participants had anti-diphtheria concentrations ≥0.1 IU/ml
by ELISA at year 8.5, with no change observed at year 10. The
single participant with ELISA concentrations ≤0.1 IU/ml was seroprotected
at each time point as assessed using the in vitro
neutralisation assay (Table 2).