COVID-19 variants

RNA sequence evolution in the COVID-19 SARS rRNA virus

    The RNA Corona virus responsible for COVID-19 SARS (Severe Acute Respiratory Syndrome) first emerged in the vicinity of Wuhan, China, in late 2019 (hence the '-19'). Its RNA sequence comprises about 30,000 A C G & U s, and Wuhan-Hu-1 [top, at 12 o'clock] is used as the reference for comparison with new strains. The sequence is catalogued in NIH's NCBI (National Center for Biotechnology Information) on-line GenBank library as accession NC045512.2. NCBI maintains the Virus Data Hub, which collates new sequence data as they emerge.

     The original Wuhan-Hu-1 virus sequence has mutated (A C G U bases in the sequence change to different letters) as it has spread through the human population. Virus mutation is extremely rapid: related lineages of the virus can be identified by shared mutations between isolates collected at different times and places, in the same way that DNA sequences are used to track family trees in humans. The diagram reconstructs the evolutionary relationships among some of these lineages through 2021. Numbers on each of the branches indicate the number of mutations that have occurred. For example, the "Iota" variant of the "Delta" strain [bottom, 7 o'clock] differs from it by (17.3 + 5.8) = 23.1 mutations. Greek letter names are assigned to major new strains, especially when its mutations affect its biology. For example, gene mutations in the Delta strain lead to changes in the critical 'Spike Protein' that affect how the virus attaches to human cells, and therefore affect its infectivity and transmission. Another Delta variant shown was isolated from a house cat in France: animal populations can act as reservoirs for viruses that produce symptoms only in humans. The original Wuhan virus appears to have arisen as a hybrid between bat and humans viruses.

    Lineages of present concern are the Delta variant [bottom, 7 o'clock], which has a higher infection rate than previous forms, and the Omicron variant [10 o'clock], which emerged in November 2021 in southern Africa and has rapidly spread to other populations. Omicron is notable for having an extremely large number of mutational differences from the Wuhan reference (~ 70), many of which occur in the 'Spike Protein' gene, and have the potential to change the way in the which the virus attacks human cells, and (or) the ability of existing vaccines to guard against it.