It's called flu. Which are basically two diseases, first the bacterial infection in all the dead cells the T-cells killed. In the lung this is pneumonia. Pretty serious stuff.

Second the rampage the T-cells are doing elsewhere to fight suspected virus cells. They might attack way too many healthy cells everywhere. This is called the cykotine storm, treated with standard cykotine storm suppressors. The virus itself is doing nothing, it just causes the immunosystem to overreact.