Marek's vaccination???

Hi! I had a beautiful hen that died two days ago. Her body was sent off for necrosis and the vet said it will take a couple of weeks for the results. I think she was egg bound and I caught it too late.

Since then I've been reading about Marek's disease and the horror stories about how bad the disease can get. Is it too late for me to vaccinate my flock. Most are between 6 to 8 months old. They are in good health. If the report comes back negative for marek's disease, can I then vaccinate my flock or is it too late.. err.. are they too old for the vaccine?

O wait.. I have 6 little chicks that are 7 weeks old. too late for them?

I'm asking because losing my chicken was heartbreaking. Since the disease is so prevalent around the country, I would really like to get all the birds vaccinated. I've read you can buy it online and give it to them yourself. I know if they have been exposed, then it probably wouldn't help, but would it help if they haven't been exposed?

Also, I'm thinking about ordering a few more baby chicks. I would like to vaccinate them. If I do get them vaccinated, could they ever mix with the un-vaccinated birds?

It seems that there is no point in vaccinating older birds because they will already have been exposed. You can find quite a discussion on the topic here https://www.backyardchickens.com/t/39918/mareks-vaccine

When you order chicks, have them vaccinated at the hatchery as day-olds before they are shipped. Then the chicks must be isolated away from the flock for two to three weeks, to build immunity. If you don't have Marek's in your flock, that's great! If the disease appears later, your vaccinated birds are much less likely to get the tumors that Mareks' disease causes. Mary