Here; an excerpt

The more transmissible variant, B.1.1.7, is already spreading rapidly in the United Kingdom, Ireland, and Denmark, and probably in many other countries. But scientists are just as worried about 501Y.V2, a variant detected in South Africa. Some of the mutations it carries, including ones named E484K and K417N, change its surface protein, spike, and have been shown in the lab to reduce how well monoclonal antibodies combat the virus. In a preprint published earlier this month, Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center, showed that E484K also reduced the potency of convalescent sera from some donors 10-fold—although he is quick to add this does not necessarily mean the mutation would cause people's immunity to the new strain to drop 10-fold.

P.1 [the Brazilian variant] adds to the concerns because it appears to have hit on a similar constellation of mutations and has emerged in a place with a high level of immunity. “Anytime you see the same mutations arising and starting to spread multiple times, in different viral strains across the world, that's really strong evidence that there's some evolutionary advantage to those mutations,” Bloom says….

(Thanks to Dr. David Ozonoff for the pointer.)