symptomatic patient on 30 december 2019 and is widely used (especially by those collaborating with gisaid) as a reference sequence. the variant first sampled and identified in wuhan, china is considered by researchers to differ from the progenitor genome by three mutations. subsequently, many distinct lineages of sars-cov-2 have evolved. notability criteria viruses generally acquire mutations over time, giving rise to new variants. when a new variant appears to be growing in a population, it can be labelled as an "emerging variant". in the case of sars-cov-2, new lineages often differ from one another by just a few nucleotides. some of the potential consequences of emerging variants are the following: increased transmissibility increased morbidity increased mortality ability to evade detection by diagnostic tests decreased susceptibility to antiviral drugs (if and when such drugs are available) decreased susceptibility to neutralising antibodies, either therapeutic (e.g., convalescent plasma or monoclonal antibodies) or in laboratory experiments ability to evade natural immunity (e.g., causing reinfections) ability to infect vaccinated individuals increased risk of particular conditions such as multisystem inflammatory syndrome or long covid. increased affinity for particular demographic or clinical groups, such as children or immunocompromised individuals. variants that appear to meet one or more of these criteria may be labelled "variants under investigation" or "variants of interest" pending verification and validation of these properties. the primary characteristic of a variant of interest is that it shows evidence that demonstrates it is the cause of an increased proportion of cases or unique outbreak clusters; however, it must also have limited prevalence or expansion at national levels, or the classification would be elevated to a "variant of concern". if there is clear evidence that the effectiveness of prevention or intervention measures for a particular variant is substantially reduced, that variant is termed a "variant of high consequence". variants of concern (who) listed below are the variants of concern (voc) recognised by the world health organization as of october 2022. other organisations such as the cdc in the united states have at times used a slightly different list; for example, the cdc has de-escalated the delta variant on 14 april 2022, while the who did so on 7 june 2022.false-colour transmission electron micrograph of a b.1.1.7 variant coronavirus. the variant's increased transmissibility is believed to be due to changes in structure of the spike proteins, shown here in green. omicron main article: sars-cov-2 omicron variant lineage b.1.1.529 the omicron variant, known as lineage b.1.1.529, was declared a variant of concern by the world health organization on 26 november 2021. the variant has a large number of mutations, of which some are concerning. some evidence shows that this variant has an increased risk of reinfection. studies are underway to evaluate the exact impact on transmissibility, mortality, and other factors. named omicron by the who, it was identified in november 2021 in botswana and south africa; one case had travelled to hong kong, one confirmed case was identified in israel in a traveler returning from malawi, along with two who returned from south africa and one from madagascar. belgium confirmed the first detected case in europe on 26 november 2021 in an individual who had returned from egypt on 11 november. indian sars-cov-2 genomics consortium (insacog) in its january 2022 bulletin noted that omicron is in community transmission in india where new cases have been rising exponentially. ba. sublineages according to the who, ba.1, ba.1.1, and ba.2 were the most common sublineages of omicron globally as of february 2022. ba.2 contains 28 unique genetic changes, including four in its spike protein, compared to ba.1, which had already acquired 60 mutations since the ancestral wuhan strain, including 32 in the spike protein. ba.2 is more transmissible than ba.1. it was causing most cases in england by mid-march 2022, and by the end of march, ba.2 became dominant in the us. as of may 2022, the sublineages ba.1 to ba.5 including all their descendants are classified as variants of concern by the who, the cdc, and the ecdc (with the latter excluding ba.3). further sublineages emerging in 2022 during 2022, a number of further new strains emerged in different localities, including xbb.1.5, which evolved from the xbb strain of omicron. the first case involving xbb in england was detected from a specimen sample taken on 10 september 2022 and further cases have since been identified in most english regions. by the end of the year, xbb.1.5 accounted for 40.5% of new cases across the us, and was the dominant strain; variant of concern bq.1 was running at 18.3% and bq.1.1 represented 26.9% of new cases, while the ba.5 strain was in decline, at 3.7%. at this stage, it was uncommon in many other countries, for example in the uk it was represented about 7% of new cases, according to ukhsa sequencing data. on 22 december 2022, the european centre for disease control wrote in a summary that xbb strains accounted for circa 6.5% of new cases in five eu countries with sufficient volume of sequencing or genotyping to provide estimates. variant of concern lineages under monitoring (who) on 25 may 2022, the world health organization introduced a new category for potentially concerning sublineages of widespread variants of concern, called voc lineages under monitoring (voc-lums). this decision was made to reflect that already in february 2022, over 98% of all sequenced samples belonged to the omicron family, and there has been significant evolution within this family. as of 9 february 2023 pango lineagegisaid cladenextstrain claderelation to circulating vocs first documentednotable features bf.7 gra 22b ba.5 sublineage 2022-01-24 ba.5 + s:r346t bq.1 gra 22e ba.5 sublineage 2022-02-07 bq.1 and bq.1.1: ba.5 + s:r346t, s:k444t, s:n460k ba.2.75 gra 22d ba.2 sublineage 2021-12-31 ba.2.75: ba.2 + s:k147e, s:w152r, s:f157l, s:i210v, s:g257s, s:d339h, s:g446s, s:n460k, s:q493r reversion ch.1.1 gra 22d ba.2 sublineage 2022-07-20 ba.2.75 + s:l452r, s:f486s xbb gra 22f recombinant of ba.2.10.1 and ba.2.75 sublineages, i.e. bj1 and bm.1.1.1, with a breakpoint in s1 2022-08-13 ba.2+ s:v83a, s:y144-, s:h146q, s:q183e, s:v213e, s:g252v, s:g339h, s:r346t, s:l368i, s:v445p, s:g446s, s:n460k, s:f486s, s:f490s xbb.1.5 gra 23a recombinant of ba.2.10.1 and ba.2.75 sublineages, i.e. bj1 and bm.1.1.1, with a breakpoint in s1 2022-01-05 xbb + s:f486p xbf gra recombinant of ba.5.2.3 and cj.1 (ba.2.75.3 sublineage) 2022-07-20 ba.5 + s:k147e, s:w152r, s:f157l, s:i210v, s:g257s, s:g339h, s:r346t, s:g446s, s:n460k, s:f486p, s:f490s variants of interest (who) listed below are the variants of interest (voi) which are recognised by the world health organization. other organisations such as the cdc in the united states may at times use a slightly different list. as of 12 october 2022, the who does not list any circulating variants of interest. variants under monitoring (who) defined as variants with genetic changes suspected to affect virus characteristics and some indication of posing a future risk, but with unclear evidence of phenotypic or epidemiological impact, requiring enhanced monitoring and repeat assessment after new evidence. as of 12 october 2022, the who does not list any circulating variants under monitoring. previously circulating and formerly monitored variants (who) the who defines a previously circulating variant as a variant that "has demonstrated to no longer pose a major added risk to global public health compared to other circulating sars-cov-2 variants", but should still be monitored. previously circulating variants of concern (voc) the variants listed below had previously been designated as variants of concern, but were displaced by other variants. as of may 2022, the who lists the following under "previously circulating variants of concern": alpha (lineage b.1.1.7) main article: sars-cov-2 alpha variant first detected in october 2020 during the covid-19 pandemic in the united kingdom from a sample taken the previous month in kent, lineage b.1.1.7, labelled alpha variant by the who, was previously known as the first variant under investigation in december 2020 (vui – 202012/01) and later notated as voc-202012/01. it is also known as 20i (v1), 20i/501y.v1 (formerly 20b/501y.v1), or 501y.v1. from october to december 2020, its prevalence doubled every 6.5 days, the presumed generational interval. it is correlated with a significant increase in the rate of covid-19 infection in united kingdom, associated partly with the n501y mutation. there was some evidence that this variant had 40–80% increased transmissibility (with most estimates lying around the middle to higher end of this range), and early analyses suggested an increase in lethality, though later work found no evidence of increased virulence. as of may 2021, the alpha variant had been detected in some 120 countries. on 16 march 2022, the who has de-escalated the alpha variant and its subvariants to "previously circulating variants of concern". b.1.1.7 with e484k variant of concern 21feb-02 (previously written as voc-202102/02), described by public health england (phe) as "b.1.1.7 with e484k" is of the same lineage in the pango nomenclature system, but has an additional e484k mutation. as of 17 march 2021, there were 39 confirmed cases of voc-21feb-02 in the uk. on 4 march 2021, scientists reported b.1.1.7 with e484k mutations in the state of oregon. in 13 test samples analysed, one had this combination, which appeared to have arisen spontaneously and locally, rather than being imported. other names for this variant include b.1.1.7+e484k and b.1.1.7 lineage with s:e484k. beta (lineage b.1.351) main article: sars-cov-2 beta variant on 18 december 2020, the 501.v2 variant, also known as 501.v2, 20h (v2), 20h/501y.v2 (formerly 20c/501y.v2), 501y.v2, voc-20dec-02 (formerly voc-202012/02), or lineage b.1.351, was first detected in south africa and reported by the country's health department. it has been labelled as beta variant by who. researchers and officials reported that the prevalence of the variant was higher among young people with no underlying health conditions, and by comparison with other variants it is more frequently resulting in serious illness in those cases. the south african health department also indicated that the variant may be driving the second wave of the covid-19 epidemic in the country due to the variant spreading at a more rapid pace than other earlier variants of the virus. scientists noted that the variant contains several mutations that allow it to attach more easily to human cells because of the following three mutations in the receptor-binding domain (rbd) in the spike glycoprotein of the virus: n501y, k417n, and e484k. the n501y mutation has also been detected in the united kingdom. on 16 march 2022, the who has de-escalated the beta variant and its subvariants to "previously circulating variants of concern". gamma (lineage p.1) main article: sars-cov-2 gamma variant the gamma variant or lineage p.1, termed variant of concern 21jan-02 (formerly voc-202101/02) by public health england, 20j (v3) or 20j/501y.v3 by nextstrain, or just 501y.v3, was detected in tokyo on 6 january 2021 by the national institute of infectious diseases (niid). it has been labelled as gamma variant by who. the new variant was first identified in four people who arrived in tokyo having travelled from the brazilian amazonas state on 2 january 2021. on 12 january 2021, the brazil-uk cadde centre confirmed 13 local cases of the new gamma variant in the amazon rainforest. this variant of sars-cov-2 has been named lineage p.1 (although it is a descendant of b.1.1.28, the name b.1.1.28.1 is not permitted and thus the resultant name is p.1), and has 17 unique amino acid changes, 10 of which in its spike protein, including the three concerning mutations: n501y, e484k and k417t.: figure 5 the n501y and e484k mutations favour the formation of a stable rbd-hace2 complex, thus, enhancing the binding affinity of rbd to hace2. however, the k417t mutation disfavours complex formation between rbd and hace2, which has been demonstrated to reduce the binding affinity. the new variant was absent in samples collected from march to november 2020 in manaus, amazonas state, but it was detected for the same city in 42% of the samples from 15 to 23 december 2020, followed by 52.2% during 15–31 december and 85.4% during 1–9 january 2021. a study found that infections by gamma can produce nearly ten times more viral load compared to persons infected by one of the other lineages identified in brazil (b.1.1.28 or b.1.195). gamma also showed 2.2 times higher transmissibility with the same ability to infect both adults and older persons, suggesting p.1 and p.1-like lineages are more successful at infecting younger humans irrespective of sex. a study of samples collected in manaus between november 2020 and january