Despite what you may read on here, many of us never have a problem with Coccidiosis and many of our flocks do not have Marek's. They are both risks you need to be aware of but many of us never vaccinate our chickens, especially the ones of us that hatch our own.
For Marek's try to limit exposure to other chickens.
For Coccisiosis, also limit exposure. As yours are only a week old, keep the brooder, coop, and run as dry as you reasonably can and keep water clean. Wet conditions can lead to problems. Also, take a small amount of dirt from where they are going to be living and give them some twice a week. That will help them build up immunity to any strain of Coccisiosis you may have in your dirt, if you have any. If you do that for three weeks they should develop immunity.
For Coccidiosis learn the symptoms and how to treat if it shows up. As long as you catch it fairly early you should not have a big problem. As long as things are reasonable dry and you keep the water clean it should not be a problem. Many of us never experience a problem.
For Marek's it depends on what strain it is and if your chickens have any natural resistance. You rarely lose more than 50%, especially with a fair number of chickens, though anything is possible.
Not with the Chicken Marek's vaccine. The vaccine used is Turkey Marek's. It does not stop the chicken from getting the disease, if they are exposed. The Turkey Marek's prevents the lesions that cause the damage from forming. Vaccinated chickens can still catch the disease and spread it, they just won't show symptoms of they get it.
