A.1 Descended from the ancestral version of the Covid-19 virus that was first detected in China, the A.1 lineage is associated with some of the earliest cases of Covid-19 in the U.S., including the outbreak in Washington state that was first detected in January 2020.
Its numbers diminished as other variants took hold in the country. B.1 Associated with the early 2020 outbreak in northern Italy, the virus developed a mutation called D614G, which helped make it better at infecting cells, allowing it to outcompete earlier variants.
The B.1 lineage went on to become the dominant version both globally and in the U.S. B.1.2 Derived from B.1, the B.1.2 variant came to account for more than 40% of U.S.