Enteric Immunization with Live Adenovirus Type 21 Vaccine I. Tests for Safety, Infectivity, Immunogenicity, and Potency in Volunteers

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Abstract
Studies were undertaken in volunteers to determine whether living adenovirus type 21 (ADV-21) vaccine could be safely administered orally to susceptible young adults. In the first study, ten volunteers were fed 106.4 tissue culture infectious dose50 (TCID50) of ADV-21 vaccine virus, and five received placebo tablets. Nine of ten infected volunteers shed ADV-21 in stools (mean duration, 10.1 days; range, 4 to 17 days). No pharyngeal excretion of ADV-21 was observed in any of these volunteers. Each of the nine developed type-specific neutralizing (N) antibodies to ADV-21. No evidence for person-to-person transmission of vaccine was observed. In a second study, volunteers were immunized with ADV-21 vaccines containing 106.8, 104.6, and 102.4 TCID50. ADV-21 N antibody responses were detected in nine of eleven who received the highest dose, six of twelve who received the middle dose, and two of twelve who were fed the lowest dose. None of twelve susceptible volunteers receiving the placebo capsule developed ADV-21 N antibodies postimmunization. This study established that the human infectious dose50 for these lots of ADV-21 vaccine was approximately 104.6 TCID50 and that the dose response to ADV-21 vaccine was lower than those previously reported for live ADV-4 and ADV-7 enteric vaccines.