Cornelius Roemer Profile picture
Nov 29, 2021 7 tweets 4 min read Read on X
Genetic diversity within #Omicron can give us clues about its age and growth rate.
Omicron's abundant spike mutations and deletions interfere with sequencing, sometimes leading to incomplete genomes.
As a result phylogenetic inference struggles, causing spurious diversity. 1/5
To explore diversity within Omicron while addressing these issues @richardneher and I built a tree ignoring
1. sites mutated with respect to reference in more than 90% of available Omicron sequences
2. homoplasic sites that often fall in dropout regions
nextstrain.org/groups/neherla… 2/
The resulting tree has one big polytomy and a small number of notable clades.
Most sequences are within one or two mutations of the main group.
Though masking might lead to underestimates of the diversity, the resulting tree suggests a recent common ancestor 1-2 months ago. 3/5
As one example for how this tree can be used, the recent Dutch sequences appear to span the globally observed diversity. 4/5
nextstrain.org/groups/neherla…
It is amazing that within one week after discovery, there are publicly available sequences from across the globe
A big thank you to all sequencing teams for sharing this data
We will keep this analysis updated and hope it is useful
Link to @nextstrain: nextstrain.org/groups/neherla… 5/5
Clarification:
The Dutch sequences were all from travellers from South Africa.
The observed diversity indicates this was not just one single group but that travellers had picked up Omicron a number of times independently from the community, presumably in South Africa.
The tree has been updated with 3 new international sequences from Spain, Czech Republic and Reunion
The Spanish sequence is on a branch with ORF1a:K564N, shared with 1 Dutch and 2 South African sequences.
Czech/Reunion have one extra mutation each that hasn't been observed so far

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More from @CorneliusRoemer

Aug 21, 2023
Here are counts of BA.2.86 and overall sequence submissions to GISAID
Note that the English sample included in week 2023-08-07 likely got expedited, so it may be best to exclude from this analysis. 1/ Image
In my very rough reading, there's not enough data yet to pin down growth advantage. It could be small or non-existent, or it could be sizeable, e.g. doubling every week.
Bear in mind that due to constant antigenic drift, there are always lineages with decent growth advantage. 2/
To really have an impact, BA.2.86 would have to become dominant, outgrowing even the fittest lineages around, e.g. HK.3 (EG.5.1 with S:L455F) or FL.1.5.1 (456L, 478R) which themselves are doubling in share about every two weeks. 3/
Read 14 tweets
Aug 11, 2023
EG.5 (and EG.5.1) has recently got attention due to being highlighted by @UKHSA and @WHO.
EG.5, which is an alias for XBB.1.9.2.5, is a sublineage of XBB characterized in particular by Spike RBD mutation F456L. 1/
EG.5 is one of the fastest growing XBB sublineages, particularly common in China where it appears to be dominant.
As EG.5 has only one RBD difference compared to the upcoming vaccine strain XBB.1.5 vaccine protection is expected to be good. 2/
While the name EG.5 may sound very different from XBB, it is important to know that this is just due to naming - EG.5 is the short form of XBB.1.9.2.5. 3/
Read 8 tweets
Apr 10, 2023
It appears that China has stopped uploading SARS-CoV-2 sequences to GISAID and now shares via its own version of Genbank: Genbase
github.com/yatisht/usher/…
I don't yet fully understand the terms under which China shares the sequences - I assume (and hope_ they are just as open as Genbank.
In that case this is a great development towards having as much SARS-CoV-2 data being free of usage restrictions as possible.
GISAID should still be able to integrate the data in their platform (unless the license prohibits it, if it's Genbank-like then GISAID can pull the data as they've done with Genbank-only published sequences).
Read 6 tweets
Nov 28, 2022
I'm seeing quite a bit of discussion about the potential impact of a big wave in mainland China on variant evolution.
I do not think a big wave in mainland China would have major consequences outside of China. 1/
While China is a big country, it has less than 20% of the global population. The rate at which new variants evolve would only increase slightly as a result of fractionally more infections worldwide. 2/
We have by now seen multiple second generation BA.2 variants evolve independently: BA.4/5 in Southern Africa, BA.2.75 in South Asia, BA.2.3.20 in the Philippines, BS.1 in South East Asia. 3/
Read 9 tweets
Oct 14, 2022
For straightforward problems, @github Copilot really rocks.
Yes, as a Python dev, I could code this up myself in less than a minute
But why spend mental energy on this if it can be auto-generated?
As a beginner, this could have easily taken me a few minutes. Now it's just seconds
And the only unnatural about this example is that I deleted the output generated by copilot before recording.
Everything else is exactly as it was when I did it.
Nothing contrived, very natural usage pattern.
It's hard to think of a better way of solving this problem.
Copilot chose a very pythonic solution.
There's a good chance handwritten solutions by many developers would be less idiomatic and more confusing.
Read 6 tweets
Oct 13, 2022
BQ.1* and XBB have different geographic foci
BQ.1* is mostly in Africa, Europe and North America
XBB in South (East) Asia
3 countries with similar levels worth watching for comparison and potential co-circulation are:
- Japan
- Australia
- South Korea
cov-spectrum.org/explore/World/… 1/ ImageImageImage
BQ.1.1 and XBB have quite a lot of spike differences and seem to have similar growth advantages - this makes them candidates for co-circulation.
We may only be able to know once we see how the variants do in countries that had a wave with the other one. 2/
Here are the mutations that only occur in one of the two variants:
XBB only: S:V83A, S:Y144-, S:H146Q, S:Q183E, S:V213E, S:G339H, S:R346T, S:L368I, S:V445P, S:G446S, S:F486S, S:F490
BQ.1.1 only:
S:H69-, S:V70-, S:V213G, S:G339D, S:K444T, S:L452R, S:F486V 3/
Read 7 tweets

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