The story begins with a patrolling the body. He is inexperienced and easily terrified when he encounters cells infected by the Influenza Virus . These infected cells behave like zombies, attempting to spread the virus to others.
Unlike bacteria, viruses must "hijack" a host cell's machinery to reproduce, which the anime depicts as the cells turning into "zombies". Hataraku Saibou (TV) Episode 3
You can find the series on platforms like Netflix or Crunchyroll. The story begins with a patrolling the body
Naive T Cell, Macrophage (major appearance), Dendritic Cell. Macrophage (major appearance)
A Macrophage appears, wielding a large weapon to clear out the virus. She identifies the virus as Type B and contacts Helper T Cell for reinforcements.