![]() ![]() Currently, there are several subvariants designated “Omicron,” including B.1.1.529, BA.1, BA.1.1, BA.2, BA.3, BA.4, BA.5 and BF.7 as well as BQ.1 and XBB. It is likely that Omicron variants will continue to emerge and develop as the pandemic continues. Omicron lineages share 39 mutations from the ancestral strain of SARS-CoV-2, and BA.1 and BA.2 also differ by 28 mutations ( Colson, March 2022 Yu, April 2022 ) - approximately twice as many amino acid differences as those that exist between the ancestral strain of SARS-CoV-2 and the first four WHO-designated variants of concern (Alpha, Beta, Gamma and Delta). WHO designated the Omicron variant (B.1.1.529) a “variant of concern” in November 2021 based on the number and location of mutations present in the spike protein, many of which had been previously associated with increased transmissibility and immune evasion, as well as epidemiological data from southern Africa suggestive of high rates of reinfection and replacement of Delta by Omicron. The numerous mutations associated with Omicron variants can impact the performance of certain molecular tests targeting the spike protein gene, as well as viral transmissibility, and neutralization by monoclonal antibodies ( see table ) or antibodies elicited by COVID-19 vaccination or SARS-CoV-2 natural infection. Source: Screenshot of CDC Nowcast data accessed May 5, 2023. indicates that vaccination with bivalent boosters is still effective against illness caused by XBB/XBB.1.5 at least for 3 months after vaccination ( Link-Gelles, February 2023 ) and that XBB.1.5 does not cause severe disease more frequently than BQ.1 ( Luoma, February 2023 ).ĬDC’s COVID Data Tracker illustrates the proportions of each of the lineages currently circulating in the U.S. However, early and limited evidence from the U.S. Health Security Agency, January 2023 Yue, February 2023 ). Limited existing evidence suggests that XBB.1.5 may be more transmissible than the XBB parent strain, due to both observed epidemiological characteristics and a higher ACE-2 binding affinity than other strains ( U.K. XBB.1.5, a descendant of the subvariant XBB, is also recombinant and is sometimes called the Kraken variant. BQ.1 and BQ.1.1 are subvariants of BA.5, whereas XBB is a recombinant subvariant combining genetic information from Omicron BA.2.10.1 and BA.2.75 subvariants. compared to other Omicron subvariants in late 2022, BQ.1 and BQ.1.1 were more highly prevalent. Some Omicron subvariants are more prevalent than others. Currently, the Omicron recombinant subvariant XBB is more prevalent in the U.S. Naming conventions for recombinant variants include an “X,” referring to the intersection of genetic material from two previously distinct lineages. Recombination events occur more frequently when community transmission levels are high. Recombinant virus: Viruses that occur when multiple variants infect the same individual at the same time and exchange genetic material with each other, changing their formulations. This term is sometimes used interchangeably with “subvariant.”Īncestral strain: The original form of SARS-CoV-2 identified in December 2019 often referred to elsewhere as the “original” or “Wuhan” strain. For example, Omicron BA.2 is an Omicron sublineage. Lineage: A group of closely related viruses with a common ancestor. This term is sometimes used interchangeably with “sublineage.” Subvariant: A subgroup of variants categorized based on genomic changes that they have in common and the time frame in which those changes appeared in tandem. Variant: A specific viral genome that contains one or more changes from the ancestral strain. Here we define key terms to discuss SARS-CoV-2 variants: ” Some variants are not associated with increased transmissibility or disease severity compared to the ancestral strain. Other variants could be more highly transmissible, cause more severe disease, or evade protection from therapeutics and/or vaccines, based on information about viral genomes or small-scale epidemiological studies, but these features may not be confirmed yet on a larger scale WHO designates these “ variants of interest. Some of these variants are more highly transmissible, cause more severe disease, or evade protection from therapeutics and/or vaccines these have been designated “ variants of concern ” by the World Health Organization. Scientists have identified numerous SARS-CoV-2 variants. Most mutations do not produce clinically relevant changes for individual infections, but occasionally mutations occur that may make the virus more infectious, cause more severe disease, evade the protection afforded by vaccines or therapeutics, or affect the sensitivity or specificity of diagnostic tools. Viruses including SARS-CoV-2 mutate over time, and as a result, new variants tend to emerge. Some sections may reflect more recent updates. This page undergoes regular review and was last comprehensively reviewed on February 24, 2023. ![]()
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