Human immune response to botulinum pentavalent (ABCDE) toxoid determined by a neutralization test and by an enzyme-linked immunosorbent assay.

To determine the immune status of persons receiving botulinum pentavalent (ABCDE) toxoid and to evaluate the effectiveness of the vaccine, we surveyed immunized individuals for neutralizing antibodies to type A and to type B botulinum toxins. After the primary series of three immunizations administered at 0, 2, and 12 weeks, 21 of 23 persons tested (91%) had a titer for type A that was greater than or equal to 0.08 international units (IU)/ml, and 18 (78%) had a titer for type B of greater than or equal to 0.02 IU/ml. (One international unit is defined as the amount of antibody neutralizing 10,000 mouse 50% lethal doses of type A or B botulinum toxin). Just before the first annual booster, 10 of 21 (48%) and 14 of 21 (67%) people lacked a detectable titer for type A and for type B, respectively. After the first booster, all individuals tested had a demonstrable titer to both types A and B. Of 77 persons who had previously received from one to eight boosts of the toxoid, 74 (96%) had an A titer of greater than or equal to 0.25 IU/ml and would not require an additional booster, according to the recommendations of the Centers for disease Control. However, only 44 of 77 (57%) had a B titer of greater than or equal to 0.25 IU/ml. In each group by booster number, even the group having had eight boosts, at least one person would require reimmunization on the basis of B titer. There was a wide range of antibody levels among individuals at the same point in the immunization scheme. Results from an enzyme linked immunosorbent assay, with purified type A or type B neurotoxin as the capture antigen, were compared with neutralization test results on 186 serum samples for type A and 168 samples for type B. Statistically, the correlation coefficients for results from the two assays were high (r = 0.69, P < 0.0001, for type A and r = 0.77, P < 0.0001, for type B). However, due to the wide dispersion of values obtained, using enzyme-linked immunosorbent assay results to predict neutralizing antibody levels is unwarranted.