ELISA for the routine determination of antitoxic immunity to tetanus.

Serum samples from 727 persons with different vaccination histories were assessed for tetanus antitoxin content in an enzyme linked immunosorbent assay (ELISA) and tested for tetanus toxin neutralization activity in mice in order to compare the results obtained by the two methods. Neutralizing antibody activities in sera from individuals previously completely vaccinated correlated well with results obtained by ELISA and the accuracy increased with increasing antitoxin concentration in serum. This correlation was observed in sera from persons vaccinated recently as well as in sera from persons vaccinated many years ago. In sera from persons with an incomplete vaccination history ELISA was found to be an unreliable tool for the prediction of in vivo results. Many of these sera had antitoxin levels by ELISA far above the in vivo values, probably due to the presence of non specific or low avidity antitoxin which is detected in ELISA. The lowest ELISA value reliably predictive of protective antibody activity in serum irrespective of vaccination history was found to be 0.16 IU/ml. It was concluded that ELISA is useful for larger population studies as an initial test, but sera with an antitoxin content below 0.16 IU/ml should also be assessed in a neutralization system.