Oral immunization against tetanus.

Model experiments in mice were used for the investigation of oral immunization against tetanus. The efficacy of oral tetanus toxoid application was tested by subcutaneous challenge (10 LD50 tetanus toxin) and antitoxin determination by L+-method. Reasonable protection could only be achieved when toxoid was in intensive contact with the mucous membranes of the oral cavity, whereas immunization by way of the gastrointestinal tract failed completely. After a single oral vaccination with 200 Lf fluid tetanus toxoid onto mucous membranes of the oral cavity the efficiency index was 75. A 100% protection was obtained in challenge after 3 applications of 200 Lf toxoid. In comparison, a single subcutaneous dose of 2 Lf tetanus toxoid resulted in an efficiency index of 100 and a single intranasal immunization with 100 Lf in an efficiency index of 93. Development of immunity after oral immunization was much accelerated if compared with parenteral immunization. 20% of the orally treated animals were immune 5 days after vaccination. After the same period subcutaneously treated animals had failed to develop any protection at all. Antitoxin titers after one oral vaccination (200 Lf) were similar to the ones after one subcutaneous dose (2 Lf). A distinct increase in antitoxin titers could only be observed when revaccination was done subcutaneously. The results obtained with mice apply analogically to guinea pigs.