TLDR (corrections welcome): D614G is a mutation relating to the spike that the virus uses to infect cells. It doesn't change the spike protein itself but opens

TLDR (corrections welcome): D614G is a mutation relating to the spike that the virus uses to infect cells. It doesn't change the spike protein itself but opens up the prongs of the spike, making the spike work better for infection. A spike that works better has been confirmed in the lab under very artificial circumstances, but it hasn't been confirmed that it makes any difference in the real world. Over time, this D614G mutation became very common, now near 100%. You might assume this is the result of natural selection, but one scientist says when the population has zero immunity, there might not be any practical difference between pretty infectious and even more infectious, so there would be no selection. Other mutations have happened too, some of which change the protein of the spike. Antibodies you already have might be ineffective (or less effective) against a modified spike protein. Antibody therapies that use a cocktail instead of a single antibody would fare better against this. Vaccines and natural infection already create a variety of antibodies. Overall the virus mutates pretty slowly, which is good. Once the population has more immunity, it might change the rules of the evolution/mutation game a bit, and things could be different then.