There are thousands of mutations which have been observed. Some are consequential - changing the virus' behaviour - others are not. What constitutes a "strain"

There are thousands of mutations which have been observed. Some are consequential - changing the virus' behaviour - others are not. What constitutes a "strain" is fuzzy, since viruses are constantly evolving and it's an artificial category or human construct. To get away from that, it's often helpful to think in terms of phylogeny or genetic relationships. You can see a phylogenetic tree of the clades (essentially a "family tree" determined through mutations of the virus) & a map showing the distribution of the different clades of the virus worldwide on GSAID platform: https://www.gisaid.org/epiflu-applications/phylodynamics/ https://www.gisaid.org/epiflu-applications/phylodynamics/