Pfizer’s coronavirus vaccine is effective against a key mutation found in variants of the virus that are spreading faster than the original strain, according to an early study.

While viruses mutate all the time, scientists worry that some of the new mutations in the novel coronavirus, specifically those in a new variant discovered in South Africa, may make vaccines less effective, Live Science previously reported. The South Africa variant, known as 501.V2, as well as  another variant discovered in the U.K. known as B.1.1.7, both seem to spread more easily than the original virus, likely because they both have some of the same mutations in the SARS-CoV-2 spike protein, the weapon the virus uses to invade human cells.