Every backyard flock has been exposed to Marek's. It's not as grim as it sounds, however, some strains can be more virulent than others and will wipe you out.
I recommend vaccinating every bird you hatch from here on out. It was also recommened to me by Peter Brown to vaccinate all of your existing birds, even though they've been exposed. When I began my vaccination protocol I followed his advice and have been very happy with the results.
It is true Marek's vaccine comes in a 1000 dose vial. There is a 200 ml sterile dilutant and another vial containing a 'wafer'. You can pop the top on the vial and carefully cut the wafer into quarters. Take 1/4 of the wafer and add 50 ml of the sterile dilutant. Discard after an hour. You can do 4 "batches" of vaccinating out of one vial.
