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T. Ryan Gregory 🇨🇦 Profile picture
@TRyanGregory
May 27 • 14 tweets • 4 min read • Read on X
Meet "Nimbus", aka SARS-CoV-2 variant NB.1.8.1.

🧵

1/ Diagram showing the ancestry of Nimbus (NB.1.8.1). The evolution of NB.1.8.1 has including three recombination events, including XBB (Kraken) and BA.2.86 (Pirola) lineages.
Evolutionary tree of SARS-CoV-2 variants showing the small fraction of diversity covered by every variant with a Greek letter except "Omicron", and the enormous diversity within "Omicron", including Nimbus NB.1.8.1.
The last variant to receive an informal nickname was BA.2.86 "Pirola" nearly two years ago, back in August 2023. Since then, it has been a prolonged "variant soup" phase, with descendants of BA.2.86 arising, gaining prominence, and then falling in frequency.

2/ Tweet from August 18, 2023 with the nickname "Pirola" for BA.2.86.
A prolonged variant soup phase involving the Pirola clan does not mean there was no within-host evolution occurring. It just meant that nothing had gotten back into the general population that could compete with the many, many descendants of BA.2.86.

3/
Nimbus (NB.1.8.1) gets its name from the type of cloud (plus it's helpful that it contains "n" and "b"). It is not just another member of Pirola clan. Nimbus is a triple recombinant that includes both Pirola (BA.2.86) and Kraken (XBB) variant ancestry. Diagram showing Nimbus (NB.1.8.1) ancestry with three recombination events.
Nimbus has been significant in parts of Asia for some time, and has since begun spreading around the world. It was labeled as a "variant under monitoring" (VUM) by WHO as of May 23, 2025.

forbes.com/sites/brucelee…
Here is a map showing the spread of Nimbus (NB.1.8.1) courtesy of variant tracker @Mike_Honey_.

While officially "Omicron" (all Greek letters were given between May and November 2021, and none since), Nimbus (NB.1.8.1) is of course very divergent from its early Omicron ancestors. Mutations over time for SARS-CoV-2, with Nimbus (NB.1.8.1) indicated.
Spike (S1) mutations over time for SARS-CoV-2, with Nimbus (NB.1.8.1) indicated.
Evolutionary tree for SARS-CoV-2 variants showing the enormous diversity of "Omicron" and highlighting Nimbus (NB.1.8.1).
In terms of current vaccines, Moderna and Pfizer target KP.2 (= JN.1.11.1.2) and Novavax targets JN.1. Recent recommendations were to keep them the same, though it looks lime they may be going with LP.8.1, which is not particularly close to NB.1.8.1.



8/nbcnews.com/health/health-…
Oh, and yes we're aware of multiple pop culture references to "Nimbus", including Harry Potter, Futurama, Rick and Morty, etc.
Here's a preprint with some more characteristics of Nimbus NB.1.8.1.

biorxiv.org/content/10.110…
Quick clarification, Kraken was specifically XBB.1.5, but the ancestors of Nimbus were XBB.1.9 and XBB.1.19. I should have worded it slightly differently as "close relatives of Kraken (i.e., descendants of XBB)".
One other clarification. JN.1, KP.2, LP.8.1, and NB.1.8.1 share key mutations so it's not that those vaccines wouldn't work against NB.1.8.1 as it is now. My point was that Nimbus is a new lineage, not just part of the same Pirola soup, and it remains to be seen how it evolves.
@pelagicbird I'll be getting a booster in any case. However I don't know that LP.8.1 is any better for what's coming than the current version. Indeed, the recommendation was to keep them the same but FDA seems to be going with LP.8.1. Might be replaced by descendants of Nimbus by then.
Here's a summary of Nimbus (NB.1.8.1) info:

theconversation.com/theres-a-new-c…

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More from @TRyanGregory

T. Ryan Gregory 🇨🇦 Profile picture
Jun 6
Nimbus (NB.1.8.1) is getting a fair bit of attention, but it's not the only SARS-CoV-2 variant worth watching. Here's a link to info about a few more, all of which have arisen either through within-host evolution during chronic infection and/or within-host recombination.

🧵

1/
First, a reminder that Nimbus (NB.1.8.1) is a triple recombinant with both BA.2.86 and XBB ancestry -- that is, it has multiple recombination events and chronic infections in its evolutionary history. Here's a thread I wrote about it:



2/
Another that is very competitive is XFG, which is a recombinant of two Pirola lineages (LF.7 x LP.8.1.2).

Head over to BlueSky to see the post by Josette Schoenmakers on the XFG vs. NB.1.8.1 battle for dominance.



3/bsky.app/profile/josett…
Read 4 tweets
T. Ryan Gregory 🇨🇦 Profile picture
Apr 29
Btw folks, what happened is that Québec saved us all from Poilievre. Bloc voters went Liberal this time to keep him out.

Ontario, not so much. Big gains for the Cons.

BC was where the NDP did best last election, and this time it went Lib and Con.
So, we essentially traded a Liberal minority with progressive parties being very influential to a Liberal minority with a huge Conservative opposition and minimal progressive representation.

The fact that 41.4% voted Con (vs. 43.5% Lib) isn't a good sign either.
Yes, I'm relieved that it's not Poilievre as PM and I'm glad he lost his seat. But beyond that, we're not in a very good place overall. The major rightward shift isn't going to be good, especially when the Liberals eventually lose to the Conservatives.
Read 4 tweets
T. Ryan Gregory 🇨🇦 Profile picture
Apr 1
It's very important to be clear about what is happening in the Canadian election and how progressives need to approach it. 🧵

The LPC surge toward a majority is due primarily to a collapse of support for the NDP and Bloc, and much less so a drop in support for the CPC.

1/ Vote and seat projections for Canada.
Vote and seat projections for Ontario.
Vote and seat projections for Québec.
This means that the Libs are mostly picking up progressive voters who are planning to vote strategically to stop the Cons. They are not picking up huge numbers of "moderate conservatives".

Cons support is generally committed but Libs support isn't.



2/angusreid.org/canadian-elect…
The *winning strategy* for Libs is to make strategic voting by progressives as painless as possible by leaning *leftward*.

The winning approach for progressive voters is to make it clear they cannot be taken for granted and do not agree with rightward drift.

3/
Read 6 tweets
T. Ryan Gregory 🇨🇦 Profile picture
Mar 19
Thoughts on pandemics, inclusion, annexation, Indigenous issues, climate, genocide, and more and the connections I see among them. I fully acknowledge that I am writing this from a position of substantial intersectional privilege.

🧵

1/
I really hoped that the (ongoing) SARS-CoV-2 pandemic would inspire us to make meaningful, positive changes in society. Indeed, early on it seemed like privileged people finally understood what it was like to lack access to things we otherwise take for granted.

2/
Sadly, but perhaps predictably, we instead rushed back to the status quo as quickly as we could. If anything, things are worse now in terms of public health, accessibility and inclusion, and global health equity. Infectious disease has been actively normalized.

3/
Read 10 tweets
T. Ryan Gregory 🇨🇦 Profile picture
Mar 8
Please, stop making these terrible arguments in order to dismiss threats of annexation by the US. 🧵

1. "He's just joking, trolling, negotiating, or being Donald."

Clearly not. Stop it.

1/
2. "Trump can't just declare war on Canada."

He wouldn't bother and he doesn't need to. The last time the US formally declared war was 1942. See every US invasion or occupation since WW2.

2/
3. "The US can't invade because of the constitution / international law."

He doesn't care about either of those things. See everything he's currently doing.

3/
Read 10 tweets
T. Ryan Gregory 🇨🇦 Profile picture
Feb 17
I'm sure infectious disease minimizers are attributing the record-shattering surge of severe flu this year to "immunity debt". Let's think this through, shall we?

🧵

1/
1. Serious mitigations ended more than 4 years ago. Why would immunity debt only kick in now? And why wasn't 4 flu seasons without mitigations enough to repay whatever "debt" there was?

2/
We wrote this more than 2 years ago.

calgaryherald.com/opinion/column…
Read 12 tweets

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