Oral immunization against smallpox.

Attenuated vaccinia strain penetrates the mucous membranes of the oral and pharyngeal cavity; local lesions are not produced, even if high doses of attenuated virus are applied. Attenuated vaccinia virus thus offers the possibility of oral and nasal immunization against smallpox in man. Several groups of monkeys were immunized by the oral and nasal route. The subsequent challenge with virulent smallpox virus resulted in strongly mitigated clinical symptoms as compared to non-immunized controls. In the human, oral immunization with live attenuated virus was affected by the administration of virus-containing tablets. The procedures caused no untoward effect in primary vaccinees. Subsequent skin testing and conventional cutaneous vaccination resulted in accelerated takes, demonstrating successful oral pre-immunization.