Can I add new chicks to flock?

[lisa69]

I am into my 4th generation of birds I hatched myself, that originally came from Greenfire. They tested positive for AVL, negative for Mareks as per PCR testing from RAL labs. But they can't type the virus, and some are less virulent than others. I have not added any new birds in 2 years. I've not had any losses or symptomatic birds in 15 months. Last fall all 28 hens where laying eggs.