STRAIN-SPECIFIC REVERSE-TRANSCRIPTASE PCR ASSAY - MEANS TO DISTINGUISH CANDIDATE VACCINE FROM WILD-TYPE STRAINS OF RESPIRATORY SYNCYTIAL VIRUS

Candidate live-virus vaccines for respiratory syncytial virus are bein g developed and are beginning to be evaluated in clinical trials. To d istinguish candidate vaccine strains from wild-type strains isolated d uring these trials, we developed PCR assays specific to two sets of ca ndidate vaccine strains, The two sets were a group A strain (3A), its three attenuated, temperature-sensitive variant strains, a group B str ain (2B), and its four attenuated, temperature-sensitive variant strai ns, The PCR assays were evaluated by testing 18 group A wild-type stra ins, the 3A strains, 9 group B wild-type strains, and the 2B strains, PCR specific to group A wild-type strains amplified only group wild-ty pe strains, and 3A-specific PCR amplified only 3A strains, PCR specifi c to group B wild-type strains amplified all group A and group B strai ns but gave a 688-bp product for group B wild-type strains, a 279-bp p roduct for 2B strains, a 547-hp product for all group A strains, and a n additional 688-bp product for some group A strains, including 3A str ains. These types of PCR assays can, in conjunction with other methods , be used to efficiently distinguish candidate vaccine strains from ot her respiratory syncytial virus strains.