Fecha de publicación: -- Fuente: WIPO "tomato" The present disclosure relates to a viral vector having an exogenous RNA segment with a hairpin-like structure, for example having two or more base-paired regions separated by one or more non-base-paired regions. The exogenous RNA segment may have a secondary structure, minimum free energy, average positional entropy or other attributes within specified ranges, or with values similar to one or more hairpin-like structures of a reference wild type virus.