Every Greek-Letter COVID Variant, at a Glance
WHO gave Greek letters to five variants of concern and to a run of 2021 variants of interest. Nothing has received a letter since Omicron.
The five variants of concern (WHO label → Pango lineage → Nextstrain clade):
- Alpha → B.1.1.7 → 20I
- Beta → B.1.351 → 20H
- Gamma → P.1 → 20J
- Delta → B.1.617.2 and the AY.* lineages → 21A, 21I, 21J
- Omicron → B.1.1.529 and every BA.*, XBB.*, JN.1 and XFG descendant → 21K onward. WHO designated it on 26 November 2021, the last Greek letter it has assigned.
The 2021 variants of interest in Nextstrain's clade list: Epsilon, Eta, Theta, Iota, Kappa, Lambda and Mu. All are former designations, and none circulates today.
What is circulating in 2026 has no Greek letter. It is all Omicron's descendants, named by Pango lineage: JN.1 (WHO's one current variant of interest), and XFG, NB.1.8.1, PQ.16.1.1 and BA.3.2 (variants under monitoring). XFG is the strain in the 2026–2027 vaccines. The full crosswalk, with designation dates, is further down this page.
Sources: Nextstrain clade_display_names.yml and WHO's variant-tracking page (updated 28 July 2026), as cited in the crosswalk below; WHO, Classification of Omicron (B.1.1.529), 26 November 2021.
Three Systems, Three Jobs
Each system answers a different question, which is why none of them replaced the others.
| WHO labels | Pango lineages | Nextstrain clades | |
|---|---|---|---|
| Looks like | Alpha, Delta, Omicron | B.1.1.7 · BA.2.86 · JN.1 · XFG | 20I · 21K · 24A · 25C |
| Who assigns it | WHO's Technical Advisory Group on SARS-CoV-2 Virus Evolution | The Pango Network — proposals reviewed openly on GitHub against published criteria | The Nextstrain team (Bedford, Neher and colleagues) |
| What it is for | Public communication about a handful of variants judged to matter — "simple, easy to say and remember labels" adopted on 31 May 2021 so that people would stop naming variants after places, which WHO called "stigmatizing and discriminatory" | Tracking genealogy at the finest resolution: "a rational and dynamic virus nomenclature that uses a phylogenetic framework to identify those lineages that contribute most to active spread" (Rambaut 2020). Thousands of lineages | Marking the big branches of the tree: "genetically well defined clades that have reached significant frequency and geographic spread" — a new major clade is named when a group reaches 20% of global sequences and is at least two mutations from its parent |
| How the name is built | The next unused Greek letter, given only to a variant of concern or of interest. WHO says the labels "do not replace existing scientific names" | A letter prefix plus a dotted numeric trail; "each dot means 'descendant of'", so B.1.1.7 is a precise position in the tree. Two root lineages, A and B | The two-digit year the clade is estimated to have emerged, then a letter: 19A, 20A … 25C, 26A. "The yearly reset of letters will ensure that we don't progress too far into the alphabet" |
| How many exist | Five variants of concern (Alpha, Beta, Gamma, Delta, Omicron) and a run of 2021 variants of interest (Epsilon, Eta, Theta, Iota, Kappa, Lambda, Mu in Nextstrain's clade list). None assigned since November 2021 | "5,300 more" designated lineages beyond the famous ones, per the Pango Network's front page | About 60 major clades from 19A to 26B (Nextstrain's clade list, September 2026) |
| Status in 2026 | Still the risk-tiering authority — but since March 2023 its designations are made by Pango name, and no VOC is listed | The name CDC and WHO use in every current table | Listed alongside the Pango name in WHO's tables ("Next strain clade" column) |
How to Read a Pango Name
Four rules cover almost every name you will see.
1. Dots mean descent
B.1.1.7 — Alpha — reads: root lineage B, its first designated descendant, that lineage's first descendant, and the seventh descendant of that. Every name carries its own ancestry — "the genius of the scheme", in the Pango Network's words.
2. Three levels, then a new letter
Names "can only run three numeric levels deep before they are aliased to a fresh letter prefix". So when Omicron's root, B.1.1.529, produced descendants, they could not be B.1.1.529.1 and so on; the alias BA was assigned, and Omicron's first branches became BA.1, BA.2, BA.4 and BA.5. When BA.2.86 in turn ran out of room, its descendant BA.2.86.1.1 became JN, hence JN.1 — "JN.1 is really BA.2.86.1.1 under the hood". The alias letters are assigned in sequence and mean nothing in themselves: JN, KP, LP, NB, PQ are simply the next available pairs. This is why every 2024–2026 lineage is an Omicron descendant even though none of them contains the letters BA.
3. X means recombinant
When two parental lineages combine into a stable, spreading lineage, "it receives an X prefix — for example XBB or XE". XBB (2022) was the first recombinant to dominate globally; XEC and XFG are 2024–25 recombinants within the JN.1 family. A recombinant's numeric trail then follows the normal rules — XBB.1.5, XFG.1.1.
4. The name is a snapshot
Lineages are designated when they are spreading, and "older names are sometimes retired or folded into their parents. A Pango name is therefore a snapshot of an evolving consensus, not a permanent taxonomic rank" (Pango Network). Two versions matter for any reported lineage — the designation set and the assignment tool — which is why CDC's variant file, as our variants page shows, folds lineages under 1% into their parents and re-publishes the table each month.
The Crosswalk: Alpha to the 2026 Lineages
One row per Nextstrain major clade that carries a WHO label or a well-known Pango name, straight from Nextstrain's own clade list, with WHO's current designation where one exists.
| Nextstrain clade | Pango lineage | WHO label | WHO status, 2026 |
|---|---|---|---|
| 19A, 19B | A, B | — (the original 2019 viruses) | — |
| 20I | B.1.1.7 | Alpha | Former VOC, de-escalated |
| 20H | B.1.351 | Beta | Former VOC, de-escalated |
| 20J | P.1 | Gamma | Former VOC, de-escalated |
| 21A, 21I, 21J | B.1.617.2 and AY.* descendants | Delta | Former VOC, de-escalated — "dozens of Pango lineages (the entire AY.* series) all belonged to Delta alone" |
| 21B · 21C · 21D · 21E · 21F · 21G · 21H | (various) | Kappa · Epsilon · Eta · Theta · Iota · Lambda · Mu | Former VOIs, 2021 |
| 21M (root), 21K, 21L, 22A, 22B, 22C, 22D, 22E | B.1.1.529 → BA.1, BA.2, BA.4, BA.5, BA.2.12.1, BA.2.75, BQ.1 | Omicron | Former VOC — the last Greek letter, November 2021; its descendants are everything below |
| 22F, 23A, 23B, 23D, 23E, 23F, 23H | XBB (recombinant), XBB.1.5, XBB.1.16, XBB.1.9, XBB.2.3, EG.5.1, HK.3 | — (Omicron descendants) | Tracked by Pango name from 2022; no new label |
| 23I | BA.2.86 | — | The saltation that produced JN.1 |
| 24A | JN.1 (= BA.2.86.1.1) | — | Variant of interest, designated 18 December 2023 — the only VOI WHO currently lists |
| 24B, 24C, 24E, 24F, 24G, 24H, 24I | JN.1.11.1, KP.3, KP.3.1.1, XEC (recombinant), KP.2.3, LF.7, MV.1 | — | JN.1 descendants; former VUMs, 2024 |
| 25A | LP.8.1 | — | WHO's May 2026 vaccine-composition antigen (see the variants page) |
| 25B | NB.1.8.1 ("Nimbus" in news coverage) | — | Variant under monitoring, designated 23 May 2025 |
| 25C | XFG (recombinant; "Stratus" in news coverage) | — | Variant under monitoring, designated 25 June 2025; FDA's preferred 2026–27 vaccine antigen |
| 25B | PQ.16.1.1 (NB.1.8.1 descendant) | — | Variant under monitoring, designated 27 July 2026 |
| 25I | BA.3.2 | — | Variant under monitoring, designated 5 December 2025 — the one current lineage descended from BA.3 rather than JN.1 |
| 26A, 26B | XFG.1.1, XFG.3.4.1 | — | The newest major clades, 2026 — XFG descendants |
Read the WHO column downward and the pattern is the whole story: five Greek letters in the fourteen months from December 2020 to November 2021, then none in the four and a half years since. The virus did not stop changing — the crosswalk shows twenty-odd major clades after Omicron — but WHO's March 2023 revision of its working definitions accepted that "the current variant landscape … is dominated by Omicron descendent lineages" and has tracked them by Pango name ever since.
The Omega Variant Does Not Exist
"Covid omega variant" is a search people run, and the answer is a flat one: there is no Omega variant, and there never has been. The last Greek letter WHO assigned is Omicron, in November 2021; the letters after it — Pi, Rho, Sigma, Tau, Upsilon, Phi, Chi, Psi and Omega — are unused. WHO's own list, updated 28 July 2026, shows no current variant of concern, one variant of interest (JN.1) and four variants under monitoring (PQ.16.1.1, NB.1.8.1, XFG, BA.3.2), every one of them named by its Pango lineage. If you meet a variant with a Greek letter after Omicron, a weather name ("Stratus", "Nimbus"), a place name, or a number that looks like a year ("COVID 2026 variant"), it is not an official designation — it is a headline. The procedural reason the letters stopped, and the current WHO list kept up to date, are on our variants page.
Frequently Asked Questions
Why do COVID variants have three different names?
Three organisations, three jobs. WHO's Greek letters (from 31 May 2021) are communication labels for variants it designates as of concern or interest; Pango names encode each lineage's ancestry at the finest resolution; Nextstrain clades mark the major branches by year and letter. One virus can be Omicron, BA.2.86.1.1 (alias JN.1) and 24A at once — "complementary, not competing", in the Pango Network's words.
What does XFG or JN.1 mean?
Dots mean descent; after three numeric levels a lineage gets a fresh letter alias (JN.1 = BA.2.86.1.1; BA = B.1.1.529); an X prefix means a recombinant of two parents (XBB, XEC, XFG). The Nextstrain clade beside it — 25C for XFG — says the group reached 20% of global sequences and was first seen in 2025.
Is there an Omega variant?
No. Omicron (November 2021) is the last Greek letter assigned; WHO lists no current variant of concern and names every current variant of interest or under monitoring by Pango lineage.
What are Stratus and Nimbus?
Nicknames for XFG and NB.1.8.1 that arose outside the official systems. WHO tracks both as variants under monitoring by their Pango names (designated 25 June and 23 May 2025).
Which system should I use?
Match it to the question: WHO's designation for risk, Pango names for what is circulating (the CDC and WHO tables), Nextstrain clades for the shape of the tree, Greek letters only for the 2020–21 history.
Disclaimer. This page explains nomenclature. It is not medical advice; no variant name tells you how ill any individual will be, and current guidance on testing, treatment and vaccination is on our treatment and vaccines pages.
Sources & References
- World Health Organization. Tracking SARS-CoV-2 variants — content last updated 28 July 2026: no currently circulating VOC; VOI JN.1 (designated 18 December 2023); VUMs PQ.16.1.1 (27 July 2026), NB.1.8.1 (23 May 2025), XFG (25 June 2025), BA.3.2 (5 December 2025), each with its Pango lineage and Nextstrain clade; March 2023 update of working definitions. who.int/activities/tracking-SARS-CoV-2-variants
- World Health Organization. WHO announces simple, easy-to-say labels for SARS-CoV-2 Variants of Interest and Concern, departmental update, 31 May 2021 — labels "do not replace existing scientific names (e.g. those assigned by GISAID, Nextstrain and Pango)"; place names "stigmatizing and discriminatory". who.int
- Rambaut A, Holmes EC, O'Toole Á, et al. A dynamic nomenclature proposal for SARS-CoV-2 lineages to assist genomic epidemiology. Nat Microbiol 2020;5(11):1403–7 — the Pango system's founding paper: constrained depth of hierarchical labels; delabelling of inactive lineages. doi:10.1038/s41564-020-0770-5 · PubMed 32669681
- Pango Network. The Pango nomenclature system — "each dot means 'descendant of'"; "names can only run three numeric levels deep before they are aliased"; "JN.1 is really BA.2.86.1.1 under the hood"; X prefix for recombinants; "a snapshot of an evolving consensus"; the relationship to WHO labels and Nextstrain clades. pango.network/nomenclature
- Nextstrain. Clade naming & definitions, SARS-CoV-2 workflow documentation — the 20%-frequency and two-mutation rules; year-plus-letter naming; subclade notation. docs.nextstrain.org
- Nextstrain ncov repository,
defaults/clade_display_names.yml— the clade-to-label list (19A–26B) reproduced in the crosswalk, read September 20, 2026. github.com/nextstrain/ncov - Centers for Disease Control and Prevention. COVID Data Tracker variant proportions — the Pango-named lineage table reproduced with confidence intervals on our variants page. cdc.gov/covid
Continue Reading
Current Variants
CDC's lineage table with its confidence intervals, WHO's live list, and why the Greek letters stopped.
Vaccines
Which lineage the 2026–27 formula targets and what the trials showed.
Symptoms
How the Omicron-era presentation differs, with the matched-cohort study behind it.
Research
Peer-reviewed findings on variants and evolution, updated weekly.
