Right, I just saw this after replying to a different comment, but I think a COV-19 type scenario is probably the most likely of a bunch of really unlikely scenarios. Its unlikely an alien virus would be able to interface with a human virus, but if they managed to exchange genetic material, then it's possible the hybrid could infect a human. The same reason makes these types of pandemics from local viruses nearly inevitable. The proximity accelerates how viruses evolve and jump species. We obviously don't know enough about life to know if viruses are a universal phenomenon such that they could interface on first contact.
It's super unlikely that a virus that evolved outside of Earth would (on its own) have a mechanism to infect cells they hadn't encountered before in order to propagate. Again, nothing is impossible, but physics, chemistry and biology would all have to line up in a very specific way for that virus to infect a human cell.
It's super unlikely that a virus that evolved outside of Earth would (on its own) have a mechanism to infect cells they hadn't encountered before in order to propagate. Again, nothing is impossible, but physics, chemistry and biology would all have to line up in a very specific way for that virus to infect a human cell.