We have heard increasingly in recent weeks about new variants (or strains) of SARS-CoV-2 detected in different parts of the world that are causing concern among scientists. These new strains appear to have become more transmissible (contagious) than previous strains. Some of the new strains may also diminish the ability of antibodies from previous infection or vaccination to recognize the virus. The greater transmissibility of these viruses means that they will likely be harder to control than previous strains. Currently we are focused on 3 main variants of concern, but it is important to note that we expect the virus to continue to evolve as it infects more people worldwide, so additional variants are likely to emerge. That means that we must not focus only on the concerning variants that have already been identified — we must also be alert to the possible emergence of more new variants.

As viral sequencing ramps up, more variants will be detected. Currently, three variants appear to be of concern: B.1.1.7, B.1.351, and P.1, first detected in the UK, South Africa, and Brazil, respectively. B.1.1.7 has an unusually large number of mutations, including many in the spike protein. Although this is the best established for B.1.1.7, all of these variants may transmit better from person to person.

There are two main concerns about new SARS-CoV-2 mutations: First, these mutations persist because they enable efficient viral transmission, either by changing the part of the respiratory tract the virus infects, or by infecting human airway cells more efficiently; Second, new mutations could accumulate to allow the virus to evade our immunity, whether generated by vaccination or natural infection.

Both of these scenarios are likely to involve substitutions of amino acids in the spike protein, which binds to receptors on our cells and allows the virus to enter and replicate. This is why strains like the UK variant B.1.1.7, and a South African variant, which have been associated with greater rates of spread since they appeared last year, are particularly concerning: the UK variant includes 8 different amino acid changes in the spike protein, several of which cluster near the part that binds to the human cell ACE2 receptors so the virus can invade.

This same part of the spike protein is also a main target of antibodies that play major roles in protecting us from disease and possibly even preventing infection. Thus, there is also concern that the accumulation of these types of spike changes may allow a new variant to escape immunity generated in response to infection with earlier virus strains, as well as to immunity generated from the spike protein that is incorporated into vaccines, which was designed with the first SARS-CoV-2 sequences nearly a year ago.