Inter-variant Recombination, Genomic Perspectives and Pathogenicity of Emerging Sub-variants of Omicron: Recent Updates and Challenges

The years 2019–2021 of the twenty-first century are synonymous with the COVID era, as the Coronavirus disease 2019 (COVID-19) wreaked havoc and continues to be aggressively persecuted. Globally, about 300 million COVID-19 cases and nearly 5.3 million fatalities have been recorded so far. Since then, the coronavirus RNA genome has rapidly mutated, giving rise to several mutant and recombinant variants. On March 9, 2022, a new recombinant known as Deltacron/Delmicron emerged due to inter-lineage recombination between Delta and Omicron. Many researchers consider it a "grey rhino" occurrence rather than a "black swan" event. However, some groups of scientists claim it is a "laboratory error". Another COVID-19 variant, XE (a recombination of BA.1 and BA.2), has been discovered, which has a transmission rate ten times higher than the fastest-spreading Omicron subvariant BA.2. Delta and Omicron, two of the most novel strains, co-circulated for many weeks in several parts of the globe, allowing for coinfections and eventual recombination. Consequently, the recombinant strains XD and XF are associated with a very high transmission rate and reduced neutralizing antibody response. Under these circumstances, researchers are rushing to develop a vaccine with high efficacy against the circulating mutants and the variants likely to emerge in the near future. This review article provides recent updates on newly identified sub-variants of Omicron with an in-depth focus on their genomic alterations, infectivity patterns, and pathogenic manifestations.