They say the VD supplementation is comparable to steroid treatment. I don't see what's to be enthusiastic about, tbh.
In the case where the Borrelia are just hiding and in a latent state, then all is a question of comparating the dynamics of the two sides: the time required by the Borrelia to wake up and proliferate, vs the time required by the vitamin D to reduce the autoimmunity to the point where the body is again desensitized about itself.
A short treatment of vitamin D would be sufficient to cure the immune problem and not long enough to allow the bacteria to take over. (Hypothetically. This is just a possibility and has to be researched, but this is exactly why I am enthusiastic.)
Also, contrary to steroidal treatment, vitamin D bolsters a part of the immunity (lymphocytes T), even if it dampens an other part. So, it would restore a balance which is lost in case of defective aquiered immunity.
Because thus vitamin D would be a great solution against autoimmune diseases, among which are a lot of the cases under the umbrella Chronic Lyme Disease (it is supposed that the borreliosis can provoke an autoimmune dysfunction that continues beyond the disappearance of the bacteria).
A lot of cases of chronic fatigue would be treated by vitamin D, which is a huge news.