Hi there, I recently lost two birds this week from Mareks disease. My flock has not been vaccinated due to the fact that I never knew about this disease. I have 6 chickens left and I also have 9 ducks. Can I vaccinate my flock now? Is it too late? What do I need to do? Please help! I don't want to lose anymore birds. If I can vaccinate them now, where should I buy this from? Thank you.