Vaccinia viruses are therapeutic tools with different biomedical applications depending on the susceptibility characteristics. For example, the strain called MVA (modified vaccinia Ankara), which is unable to replicate in mammalian cells, triggers a potent immune system response and is used to develop vaccines against COVID-19 or AIDS. In contrast, other strains such as Western Reserve (WR) or Copenhagen (Cop), which replicate efficiently in tumour cells, are used to develop cancer treatments.