TheRobotanist

Viruses can not survive in space. Viruses require a host in order to live, and most viruses can only survive for a few hours without a proper host cell. Bacteria on the other hand may be able to survive. Some species have been shown to go into dormant states when there is a lack of nutrients, and these bacteria can survive in extreme environments. As for alien viruses, initially we would be immune. Viruses are extremely specific and look for certain cells within certain hosts. Viruses use receptors located on the plasma membrane of the cell. And these receptors are ones needed for the survival of the cell, so they can't simply evolve to a point where they no longer have the receptor. We'd be immune until a point where the virus has mutated and performs a "species jump" in which it can now infect humans. We've seen it on our planet. Ebola and Swine flu mutated to the point where they could bind to human receptors in certain cells.