Antibody response of pregnant women to two different absorbed tetanus toxoids.

The antibody response in pregnant women vaccinated with either of two different adsorbed tetanus toxoids has been studied. One vaccine (A), prepared by toxoiding purified tetanus toxin followed by its adsorption onto calcium phosphate, exhibited a low titre expressed as international immunizing units, 69 IIU/0.5 ml. The other vaccine (B), prepared by purifying formalinized crude tetanus toxin and adsorbing it onto aluminium phosphate showed a high titre, 212 IIU/0.5 ml. No significant differences between titres of circulating antibodies were obtained after the first injection of either vaccine, but titres after the second injection were much higher for vaccine A as compared with those obtained using vaccine B. The results showed that the immune response in human beings is not correlated to titres expressed in IIU. These results confirm that other methods should be adopted for evaluating the potency of vaccines. A simplified technique based on the comparison of circulating antitoxin levels after vaccination of mice has recently been proposed.