Viruses get small mutations as they multiply. By now, there is likely huge amount if unique viruses, not a single one. But, most mutations don't actually change anything because they might hit non coding part or maybe she mething unimportant so for the purpose of our communication we lump them together and call them strain.
Most of the time we only start discerning differences when they change the virus behaviour in an interesting way, and most of interesting stuff is around how it propagates, what it does to us and what it is susceptible to.
Viruses get small mutations as they multiply. By now, there is likely huge amount if unique viruses, not a single one. But, most mutations don't actually change anything because they might hit non coding part or maybe she mething unimportant so for the purpose of our communication we lump them together and call them strain.
Most of the time we only start discerning differences when they change the virus behaviour in an interesting way, and most of interesting stuff is around how it propagates, what it does to us and what it is susceptible to.