Nice game :) The only thing that kinda bothers me is when the leukocyte is on one side of the screen and the viruses are on the opposite side, it takes way too long to reach them... But I don't know if it's a bad thing or if it's just me 😅. The breathing sound was a really nice touch (I wish there were also some coughs when it starts getting hit with the viruses)
Off-topic 1: I just remembered I made a game with the same name when I was a kid (mine was like a pacman where you could push the walls)
Off-topic 2: Fun fact, someone made a NES game a while ago that had the same concept of a leukocyte protecting lungs from coronaviruses: https://romekrjm.itch.io/immunatio