Any proof that it went viral or it is just a marketing term?
The problem is that there are too many enemies and unlimited bullets, so the best strategy (in a keyboard) is to press:
up-space-up-space-up-space-up-space-up-space-...-down-space-down-space-down-space-down-space-down-space-down-space-down-space-...-up-space-up-space-up-space-up-space-up-space-...-down-space-down-space-down-space-down-space-down-space-down-space-down-space-...-up-space-up-space-up-space-up-space-up-space-...-down-space-down-space-down-space-down-space-down-space-down-space-down-space-...-up-space-up-space-up-space-up-space-up-space-...-down-space-down-space-down-space-down-space-down-space-down-space-down-space-...-up-space-up-space-up-space-up-space-up-space-...-down-space-down-space-down-space-down-space-down-space-down-space-down-space-...
and form a wall of bullets, without aiming. You should reduce the number of simultaneous bullets, or discount a small amount of health for a miss.
For the theme of the game, I think it's better to reduce the amount of bullets, because vaccine availability is not infinite.
Anyway, it seam to be too short, only 30 seconds. I'd like at least 5 minutes.