The scientific community is still studying the mechanisms by which specific mutations alter the virus’s ability to infect people. Most work is focused on changes to the amino acids that make up the viral Spike (S) protein, which is responsible for attaching the virus to cells so that it can enter and infect them. It seems likely that some changes to the structure of Spike could allow it to attach more efficiently to human cells, which could lead to greater transmissibility. Some mutations may also change the structure of the Spike protein in a way that makes it more difficult for antibodies to attach to it. This would help ‘hide’ the virus from the immune response. It is less clear whether mutations in the current variants of concern specifically alter antibody recognition to a meaningful degree.

Current evidence suggests that mutations in B.1.1.7 allow increased viral replication—and larger viral loads—in the upper respiratory tract of infected persons. This likely accounts for the increased transmissibility, at least in part.

So far, one mutation, D614G, that occurred early last year quickly became the predominant strain worldwide. It allows the virus to replicate more efficiently in the upper airway to enhance shedding and the efficiency of transmission. Fortunately, this substitution does not render the virus resistant to the antibodies generated in vaccinated persons. Likewise, another substitution in the spike, N501Y, which is shared by both the UK and S. African variants, does not allow the virus to escape neutralizing antibodies produced in response to vaccination.