What was it supposedly vaccinated against? Usual vaccinations are Marek's and there are some others, but I don't believe coccidiosis vaccine is standard. Bloody poo sure sounds like coccidiosis.
How old is the chick? Are they on medicated feed? With Amprolium?
Either way, you need to get some more anti-coccidiosis stuff down this little guy - either get some Sulmet or Corid into their water ASAP to knock it down. If they are on medicated feed, the continuous low-level amprolium should also help keep it under control.
If it's not coccidiosis causing the bloody poo, it could be lots of other potential things, but coccidiosis is the most common. It could also have a secondary bacterial infestation in the gut due to coccidiosis - my flock ended up with coccidiosis + clostridium at the same time!
If you have any antibiotics on hand, it probably wouldn't hurt to give this little guy some - if it's clostridium you need penicillin, bacitracin, or neomycin to treat it. Aureomycin and Tylan aren't effective against clostridium (according to my Dr. vet at our state univ.).
However, since you don't know what it is for sure, I'd throw the coccidiosis meds at him (Corid or Sulmet) and make sure he's actually drinking the medicated water, AND if you aren't on medicated feed, switch to that immediately. Past that, it's sort of hit or miss with any additional antibiotics, but the most important thing is to make sure he's getting the coccidiosis meds into his system. If he's not eating/drinking, you can make a "drench" and dribble some down his beak to make sure it gets into his body. The instructions for both methods (drinking water or drench) should be on the bottle of whatever you get (Corid or Sulmet).
Good luck, keep us updated, OH, and make sure he is kept warm - is the heat lamp still on?