Genetic stability of RSV-F expression and the restricted growth phenotype of a live attenuated PIV3 vectored RSV vaccine candidate (MEDI-534) following restrictive growth in human lung cells.

•MRC-5 cells provided restrictive growth environment for RSV vaccine candidate.•Evaluated stability of RSV-F expression and maintenance of attenuation phenotype.•Minor decline in attenuation and RSV-F expression after 23 passages in MRC-5 cells.•Modified virus still able to elicit protective anti-RSV immune responses in hamsters.