The Guardians of the TWiV-o-verse discuss the process of codon deoptimization for the production of experimental infectious attenuated viral vaccines, and how a respiratory syncytial virus with 619 base changes was rescued by genomes with very large internal deletions.

The TWiVologists discuss the finding of a second transmissible cancer in Tasmanian devils, and development of new poliovirus strains for the production of inactivated vaccine in the post-eradication era.