Can a virus that is not very transmissible but very deadly evolve to become less deadly and more transmissible?

Yes, that can happen. Viruses evolve through natural selection, and their evolutionary trajectory depends on factors like host survival, transmission opportunities, and mutation rates.

A virus that is highly deadly but not very transmissible faces a major limitation: if it kills its host too quickly or before spreading effectively, it may not persist in the population. Over time, evolutionary pressure may favor mutations that allow the virus to spread more efficiently, often by reducing its lethality or making infections last longer with milder symptoms, increasing the chance of transmission.