Pango lineage names
A Pango lineage name comprises an alphabetical prefix, denoting the parent lineage, followed in most (but not all) cases, by one or more numerical suffixes separated by dots. Each dot in the lineage name is effectively shorthand for “gives rise to” or “descendant of”. Hence B.1.1.7 is the 7th named descendant of lineage B.1.1, which was the first named descendant of lineage B.1, and so on.
To prevent lineage names from becoming too long, a system of aliasing is used. For example, C.1 is used instead of B.220.127.116.11, with C being an alias for B.1.1.1. The alphabetical prefix given to each lineage or alias is determined by a set of naming rules. For example, after prefix Z has been used, the prefixes continue with AA, AB,…, AZ, BA, BB,…, ZZ, AAA,….etc.
Lineage A and lineage B can be used without a numerical prefix, as these are special cases that lack an unambiguous ancestor lineage. Recombinant lineages represent another special case, as they have more than one ancestral lineage; these are designated by the letter X and prefixing of recombinants follows the sequence XA, XB, XC,…, XAA, XAB, etc. Information about the ancestry of recombination lineages is provided in the lineage description list. Full details of the naming rules are available here.