"vastly differ" is grammatically correct and can be used in written English.
It is often used to indicate a significant difference between two or more things. Example: The opinions of the two political parties vastly differ on the topic of immigration reform.
However, experimental, analytical and numerical results for the critical edge-dislocation dipole annihilation distance vastly differ.
Either Niven and I vastly differ on what constitutes a revelation, or else she's keeping the better ones to herself.
However, it has been earlier noticed that the overall pedestrian kinematics response may vastly differ if the lower legform impactor hits a car with a high bumper.
Though it seemed at the time to be a battle between two opposing worldviews, the truth is that the two candidates did not vastly differ in that first debate.
The reason Confident Cannabis' data is so important is that the effects of marijuana can vastly differ depending on the species (sativa or indica), strain, and quality.
Brought on by changes in technology, generational differences, values, skills gaps, organizational structure and more, its future as an industry may vastly differ from its past.
Two very different men, then, with vastly differing philosophies.
We describe the generation of multiple, unique small peptides nine to thirty-four acids acins in length which, when labeled with the radioisotope 32P, bind with vastly differing efficiencies to cell lines derived from different colon adenocarcinomas.
Button tried two different sets of the 'hard' tyre in practice with vastly differing results.
It is only fitting then that Sandra Oh also portray an agent whose pathology vastly differs from the prototypical detective drama lead, effectively making Eve Polastri completely different from all of her predecessors.
There were vastly differing accounts of the toll.
