SARS-CoV-2 mutates constantly. Like, if you infect somebody, there's about a 50% chance that the virus they got from you has a mutation compared to the one that infected you. Seriously, two mutations a month in every chain.
The rate is so fast that they can sequence the virus from individual patients to determine who was infected in one cluster, and who got infected elsewhere.
Almost all of these changes have no impact. One, "D614G" affected the spike protein and seems to make it work better, this is the variant that spread through much of Europe and the US.
Now there appears to be another variant that started in Spain this summer and is spreading through Europe. They don't yet know if or how this affects contagion or mortality. [Background note - if it's spreading this fast and replacing other variants, it's almost certainly more contagious, they're just being cautious until they have more data.]
I think it's very likely that this version is more contagious and will continue to displace other variants, but too early to tell if it makes the disease milder, worse, or no change.
I read the article. Frustrating, there's absolutely no mention there or that I can find on Google for the prevalence of these variants in the US. But given that they've reached New Zealand already, it's certainly circulating here.
It is based on the D614G mutation, i.e. D614G is a parent of this clade.
It seems to increase its share of the virus in countries at a rate of about 50% per week. With that happening in multiple countries, it's almost certain that this variant spreads more rapidly.
No info at all yet on severity or mortality (for better or worse), and too early to tell if the new strain is one of the contributing factors to the major upticks in most European countries over the last three months. My guess is yes - even a 10% increase in contagion would cause a big change in the trajectory of the epidemic, and that rate that this displaces other variants suggests that it's a lot more than 10%.