Combined active-passive immunisation of horses against tetanus.

The protection afforded by active, passive and combined active-passive methods of immunisation against tetanus was examined in previously unimmunised horses. Three groups of horses were injected; one with tetanus toxoid alone, one with tetanus antitoxin alone and one in which the tetanus toxoid and tetanus antitoxin were injected simultaneously. The protection afforded was determined by monitoring the levels of antitoxin achieved in the horses by each of these methods. The results obtained demonstrated the effectiveness of the combined active-passive method in affording rapid and prolonged protection and enabled the examination of some of the factors involved in active and in passive immunisation when used alone. The advantages obtained by the use of the combined active-passive method in protecting unimmunised horses suddenly placed at risk to infection are outlined.