Thread by @CorneliusRoemer

Variant heads-up to the virologist community:
A new delta sublineage AY.33 has been designated that (to me) appears to be the most critical delta sublineage designated so far. 1/n 🧵
(journos please don't yet write about it, this has not been scrutinised by the science community)

The defining Spike mutation is S:Q613H, a mutation that has already been studied in the context of other variants due to it's closeness to the mutation S:D614G which got fixed last summer.
The other spike substitutions on top of standard Delta are S:T29A, S:T250I, S:T299I. 2/

This lineage grabbed my attention not because of its high growth rate but because of its high number of extra spike mutations that is a clear outlier on the current delta tree (see screenshot). 3/

The lineage is most common in Belgium but also growing in Denmark, the Netherlands, Germany and Switzerland and has already been observed in more than 25 countries.
The first observation was in Japan mid-June in a traveller from Morocco. The second observation was in Morocco. 4/

Using timetree, the lineage seems to have arisen in April/ May. Belgium has strong ties to Morocco so it's plausible that the lineage is widespread in North Africa where unfortunately there is very little sequencing activity (last sequences is 3mo old and this precise lineage) 5/

At this point in time, it's difficult to estimate growth advantage because in no country has this lineage reached more than 10% and we only have a few weeks of data.
But using naive methods, it's plausible that the transmission advantage could be between 10-70%. 6/

Comparing transmission advantages it's interesting to see that the growth rate seems to be higher in countries with higher vaccination rate
Spain: advantage ~70% (left)
Denmark: ~30%
Belgium: ~30%
Germany: ~20%
Switzerland: ~10% (right)
Could this be a vax escape lineage? 7/

If I was a lab scientist, I'd take a close look at this lineage and study neutralising antibody titers.
Any comments are very welcome! If you think there's something fishy going on that could explain this, please comment! 8/

You can find further details here in the designation issue (plus a list of strain names that are part of it)
github.com/cov-lineages/p…

Just to be clear, I'm not certain that this lineage is going to be the next thing but I do see a certain chance that it is. I think it should be studied. You never know with new lineages whether it's a chance event or not.