Well established azalea has white growths on the branches. The new leaves look healthy at the tops of the branches but when moved aside and underneath, you can see the branches that look dead without leaves and the white growth covering the branches.
Branches Have Some White Looking Growth
Certified GKH Gardening Expert
It could be mealy bugs, but there are several other pests it could be. All of them can be treated with neem oil. These articles will help:
If the white growth is powdery in nature, it is powdery mildew, which can also be treated with neem oil.