AY.4 Delta sub-lineage now predominant in UK and Australia, rising in the US

Africa, America, Asia, Australasia, Australia, AY.4, B.1.617.2, B.1.617.2.4, Coronavirus, Delta-AY.4, Europe, Infection, Transmission, UK, USA

A post on the AY.4 sub-lineage of the Delta Sars-Cov-2 variant. Also known as B.1.617.2.4, this sub-lineage hasn’t received a lot of press attention yet, but it seems to have become the biggest sub-lineage of Delta across the globe so far. 

In the USA, the Delta AY.4 sub-lineage is currently appearing in about 20% of sequences (light blue area) according to Outbreak.info:

AY.4 Delta Sub-lineage at 19 percent of sequences in the USA


In the UK, AY.4 currently appears in about 46% of samples (light blue area), and is now outcompeting B.1.617.2 (dark blue area).

AY.6 seems to be coming up on the rails though at 3%:

AY.4 Delta Sub-lineage at 46 percent of all UK sequences


In Australia, AY.4 (dark blue area) clearly predominates over B.1.617.2 (light blue area) with 67% of sequences, B.1.617.2 is at 16% and AY.12 is at 10% :

AY.4 Delta Sub-lineage at 67 percent of sequences in Australia


In the USA, the estimated number of AY.4 cases was over 80,000 in early August 2021:


In the UK, the estimated number of AY.4 cases was about 13,000 in late August 2021


In Australia, the estimated number of cases was over 600 in late August 2021


In the USA, the demographics for AY.4 show it spreading across almost all age ranges,


But in the UK, AY.4 seems to be spreading amongst young children:


And in Australia, AY.4 seems to be spread across all age ranges:


The global reach of the AY.4 sub-lineage is really quite astounding considering it’s relatively recent appearance:



Further reading: New AY lineages and an update to AY.4-AY.12


Many thanks, as always, to the teams at Outbreak.info and covSpectrum.org for their hard work in compiling this data.




Image by Free-Photos from Pixabay

** This post was originally published on August 29, 2021 **