Scientists debate whether viruses are alive. A single-stranded RNA virus is a string of dead proteins surrounded by a membrane, with abnormal proteins attached to the surface of the viral membrane to facilitate invasion of a cell. A virus replicates by division, inside a cell, using the energy of the host cell—thus, cannot be killed—it can only be neutralized or reach a dead end in replication with time, treatment, or vaccines.
Host cells can be normal cells or other pathogens; and when a virus is hosted by an intracellular pathogen, the virus can spread in the body and cause enhanced damage consistent with the targets and predilection of the intracellular pathogen.
Covid-19 may impact different patients differently, consistent with the differing impact of host pathogens, and the cumulative infectious burden.