"ongoing" means that something is still happening as a continuous action.
"variability" means that something includes a lot of different results/options.
"study", as a noun, means to do research of some kind.
--> so "an ongoing variability study" together is referencing research about the levels of change in a subject that has already started and has no completion date as to continue the monitoring of said changes.
"a long way off" means that the end/outcome is very far away in time and without any estimation of completion either.