Fig. 1

The course of viral infection in the host cell. Viral infection in the human body begins when viral hemagglutinin protein (HA) (a) binds to a glycolipid receptor on the cell surface. It promotes the fusion of viral cell membranes with the host cell. Once a virus enters viral genetic material (b) into the host cell, its replicates, and mRNA (c) is synthesized and converted to viral proteins. RNA viruses (like flu, SARS-CoV-2) can use their RNA to directly create countless new viruses in the host cell. DNA viruses are always making RNA copies, but rarely reverse process is occuring. Except for some retroviruses (HIV/AIDS), they copy their RNA into DNA. mRNA takes over the cell’s protein-making machinery to rapidly build a new amount of viruses. Subsequently, the synthesized viral genetic material and proteins are assembled (d) to form virions that help bud with neuraminidase (NA) and separate from the host cell. At the same time, the immunization takes place in the cell (e), the host cell begins to produce antibodies against the virus