The studies published in NEJM showed an approximate 6-fold (Moderna) and 3-fold (Pfizer) reduction of neutralizing antibodies against the South African variant of the SARS-CoV-2 virus. The researchers emphasize that an analysis on a larger cohort is essential to definitively determine whether the Moderna and Pfizer vaccines are effective against the South African variant (B.1.351).
https://www.nejm.org/doi/full/10.1056/NEJMc2102017?query=featured_home
https://www.nejm.org/doi/full/10.1056/NEJMc2102179?query=featured_home