The name of the mutation, E484K, refers to an exchange whereby the glutamic acid (E) is replaced by lysine (K) at position 484.
E484K has been reported to be an escape mutation (i.e., a mutation that improves a virus's ability to evade the host's immune system) from at least one form of monoclonal antibody against SARS-CoV-2, indicating there may be a "possible change in antigenicity". The P.1. lineage described in Japan and Manaus, the P.2 lineage (also known as B.1.1.248 lineage, Brazil) and 501.V2 (South Africa) exhibit this mutation. A limited number of B.1.1.7 genomes with E484K mutation have also been detected. Monoclonal and serum-derived antibodies are reported to be from 10 to 60 times less effective in neutralizing virus bearing the E484K mutation. On 2 February 2021, medical scientists in the United Kingdom reported the detection of E484K in 11 samples (out of 214,000 samples), a mutation that may compromise current vaccine effectiveness.