Do I treat for Cocci when some are vx & some not?

[Knock Kneed Hen]

I found a bloody stool in my pullets pen today. Most of my chicks were vaccinated against coccidiosis but I have 5 out of the 19 they weren't. Should I assume it's one of the five, pull them out, and treat them with Sulmet?

Please advise.

 

[PaulaJoAnne]

No vax is guarenteed 100%