While there's some expected variation in the SARS-CoV-2 viruses, determining what constitutes a new "strain" is not an exact science. Some people are already trying to say there are multiple "strains" of SARS-CoV-2, but it doesn't really have any differentiating properties other than slightly different genes that can be identified via sequencing. Probably just propagations from a few early super-spread events and not worthy of being identified as their own "strains" when their genetic differentiation isn't much different than what you see between two individuals.
Basically we currently have no reason to believe that SARS-CoV-2 will need to target multiple strains. We can't really even act like multiple "strains" exist until we see some differentiating property.
Mutation is the game that is fundamental to the success of viruses. They use host cells and don't have to worry about a mutation being detrimental to cells, since they have none.
It was probably over a month ago that someone released a study which tracked the spread of the virus worldwide. He produced a diagram similar to the tree of life which showed the different "strains" throughout the world. His contention was that there were six identifiable strains. The criticism was whether it was was six or sixty different strains one could identify on the diagram. It is more semantics than anything else.
Identifying mutations is now a precise and computer driven exercise, but implementing vaccines is far more complex. There is tremendous variability among humans, so finding a vaccine that will be effective for them and not harm them is problematic, especially when the virus is a moving target.