I liked the obstacles which seemed to be randomly generated. And there was always some sort of gap so if you couldn't shoot down the blood cells you could move around them. There was some kind of strange satisfaction when shooting the red blood cells, but that might just be because it adds to your score.
I'm not too big a fan of being a virus, especially if it's Covid. Also, because the projectile is so small it's difficult to tell when you can fire or not, or whether you have just fired.
If I had to suggest one improvement it would be making the projectiles bigger or giving more of an indication as to when a bullet has been fired. If I could make two, my second would be to make the game more challenging somehow, because once you get the hang of it the game feels relatively easy.
Nice game, great job!