Yes, the frequencies can be used preventively as well. Kind of like a vaccination thing.
Please, let me give you an example:
If I was to attend the Olympic Games in Brazil and didn’t want the Zika virus brought with me home, I would just run my Zika frequency, until I got home again.
Or if I didn’t want to be stung by mosquitoes in the first place, I would just run another frequency etc.
It can also be used to kill moulds, pests, entrainment, etc