Attenuation of Rubella Virus by serial Passage in Primary Rabbit Kidney Cells: III. Clinical Trials in Infants

Extract: High passage Cendehill strain of rubella virus, possesing in vivo and in vitro characteristics of an attenuated virus, was tested for efficacy in 28 seronegative infants, 3 to 23 months old. Thirteen seronegative infants received one subcutaneous injection of 0.5 ml of the vaccine preparation containg 103.7plaque-forming units (PFU) per ml. Fifteen seronegative infants served as controls for viral spread and were kept in intimate contact with the vaccinees for a period of 6 weeks.All thirteen vaccines developed high levels of hemagglutination-inhibiting antibodies, from 1/128 to 1/2048, confirming the immunogenicity of the vaccine. No clinical reactions were observed in the vaccinees. The fifteen contacts remained seronegative, indicating that no viral spread occurred from the vaccinees to the susceptible contacts.The present clinical trial provides evidence that high-passage Cendehill strain presents characteristics of immunogenicity, nonreactogenicity and noncommunicability, making it a prospective candidate for a live attenuated rubella virus vaccine.Speculation: When the results of preliminary immunization trials with the attenuated Cendehill strain of rubella virus are confirmed in larger groupt, this strain may meet all the criteria required for a safe and efficient immunizing agent against rubella.