CLINICAL AND IMMUNOLOGICAL RESPONSE OF INFANTS AND CHILDREN TO ADMINISTRATION OF LOW- TEMPERATURE ADAPTED RESPIRATORY SYNCYTIAL VIRUS

Thirty-nine infants and children 6 months to 13 years of age received live 26°C grown respiratory syncytical (RS) virus (strain A2) by the oropharyngeal and nasopharyngeal route. RS virus was recovered from 22 individuals and 17 of these showed a significant rise in CF and/or plaque reduction serum antibody. Twelve of those from whom virus was recovered and an additional three from whom virus was not recovered showed a threefold or greater rise of RS nasal neutralizing activity. Thus 26 of the total showed some evidence of having been infected with the ES strain. The rate of infection was significantly greater in infants and children under 2 years of age than in older children. Infection in individuals older than 8 months of age was asymptomatic. Three infants infected with the vaccine strain had relatively minor respiratory tract illness. The findings from this study indicate that the low-temperature adapted virus retains a low level of virulence which is expressed only in individuals undergoing primary infection. Nonetheless, these studies have shown that it is possible to induce local and systemic immune responses to RS virus by means other than fully virulent natural infection.