Update on a couple of new SARS-CoV-2 strains that have been discovered recently in the UK and South Africa. There is some talk that the UK variant (and the SA one) is significantly more transmissible than the predominant strains that have been in the UK, but that's based on growth rates of people with the variant (which could be related to superspreader events) not on any controlled experiments in vitro or in animals. UK PM Boris Johnson's comment about it being 70% more transmissible is a guess, but it's certainly a factor in the UK clamping down more strongly on the populace.
No info yet on impacts on severity of the infection, but past mutations have not had any apparent effect. Similarly, even though there are a bunch of mutations, including in the spike protein, Trevor Bradford, noted virologist (his Twitter thread on this is linked below), said he's "not concerned that these variants will significantly reduce vaccine efficacy in the 2021 rollout."
He is concerned, though, in the longer term, with "antigenic drift," wherein the virus could cumulatively mutate enough to become less susceptible to vaccines or antibody treatments, perhaps necessitating reconfigured vaccines every few years (which would not be hard to make - would be similar to the flu), as has been seen in other coronaviruses, but we don't know if SARS-CoV-2 will behave like those or more like SARS/MERS which didn't appear to mutate much before dying out.
https://www.bmj.com/content/371/bmj.m4857
https://www.nytimes.com/2020/12/19/world/europe/coronavirus-uk-new-variant.html