What do we know about Omicron? I fear most ppl are unfortunately too optimistic. They're missing the Key Omicron Question.
Here's a summary of what we know about Omicron, and the key question that remains unanswered:
Here's a summary of what we know about Omicron, and the key question that remains unanswered:
2 numbers matter in epidemiology: the transmission rate and the fatality rate.
The transmission rate tells you how many people are likely going to catch a virus, and how hard it will be to fight it.
Once you catch it, the fatality rate tells you how bad it will be.
The transmission rate tells you how many people are likely going to catch a virus, and how hard it will be to fight it.
Once you catch it, the fatality rate tells you how bad it will be.
Then there's 2 complications: these numbers interact in weird ways.
1. Ppl believe that viruses that become less lethal spread better.
2. Yet a less lethal virus might end up killing more.
How do we make sense of it all? Let's dive deep
1. Ppl believe that viruses that become less lethal spread better.
2. Yet a less lethal virus might end up killing more.
https://twitter.com/tomaspueyo/status/1355214343714058244?s=20
How do we make sense of it all? Let's dive deep
1. Tranmission rate
This thing is growing FAST
(source:
This thing is growing FAST
(source:
https://twitter.com/trvrb/status/1469157783224217601?s=20)
The transmission rate (here Rt, how many ppl infected by a source infection) is 3-4x higher than for Delta! OMG! Is Omicron 3-4x more transmissible?
Hold on a sec.
Hold on a sec.
With an R0 of 6, Delta is already among the most contagious viruses we know. If Omicron was 3-4x more contagious, it would be the most contagious virus we've ever seen. Way more than smallpox. Unlikely. So what might be going on?
Immune escape
Immune escape
Maybe Omicron is not spreading faster than Delta because it's more contagious. Maybe it's just better adapted to its environment: one where everybody is immune, either through vaccine or previous infection
Most ppl in South Africa and EU are indeed immune
Most ppl in South Africa and EU are indeed immune
https://twitter.com/TWenseleers/status/1466502050280353799?s=20
This graph shows the possible scenarios. Omicron is on the black line. If it had the same R0 as Delta, it could be 3x more contagious if it escaped immunity 40% of the time.
It could be half as contagious with an 80% escape.
So how much does it escape immunity?
It could be half as contagious with an 80% escape.
So how much does it escape immunity?
A lot. A bunch of lab tests have all seen the same thing: substantially fewer antibodies (up to 40x)
Now antibodies are not the only immune defense, and 40x fewer antibodies doesn't mean 40x less antibody defense. Is there any data from the wild? Yes
Now antibodies are not the only immune defense, and 40x fewer antibodies doesn't mean 40x less antibody defense. Is there any data from the wild? Yes
After 6 months, 2 doses of Pfizer give you a 60% lower chance of infection (not hospitalization, that's much higher), but for Omicron it's probably ~40%. So it would be 1/3 less efficient.
FWIW the wisdom of the crowd predicts that Omicron's R0 will turn out to be about the same as Delta's, at ~6
(source: metaculus.com/questions/8755…)
(source: metaculus.com/questions/8755…)
OK so Omicron is probably ~as contagious as Delta (+/-) but escapes immunity. Makes sense since the virus has mutated SO MUCH. Look at all the mutations compared to Delta
(source:
(source:
https://twitter.com/mugecevik/status/1466845357686640640)
This virus comes from a completely different branch! It appears to have evolved in parallel, from an early variant, and is very different from from the original, Alpha, and Delta.
Is this a sign? Maybe we've finally found this elusive virus that evolves to be less virulent?
Is this a sign? Maybe we've finally found this elusive virus that evolves to be less virulent?
It wouldn't be without precedent. Look at what happened in the 1918 flu: the 3rd wave killed much less, and then it disappeared.
Is this happening now? Is this virus bypassing immunity, infecting everybody, but not killing them, and strengthening their immunity along the way?
Is this happening now? Is this virus bypassing immunity, infecting everybody, but not killing them, and strengthening their immunity along the way?
2. Fatality Rate
We're *just* at the time when we should be seeing deaths going up. Nothing so far, but it's to be expected. The next week will be defining.
We're *just* at the time when we should be seeing deaths going up. Nothing so far, but it's to be expected. The next week will be defining.
What are predictors of deaths? Hospitalizations. These are indeed growing in SA.
The jump happened on Nov 27th. 2 weeks to death is usual. So we should expect deaths to go up. The question is how much.
The jump happened on Nov 27th. 2 weeks to death is usual. So we should expect deaths to go up. The question is how much.
ICU and ventilator patients are much lower than Delta at the equivalent moment. We can assume this will continue, which means there will be fewer deaths. YAY!
The community agrees: it thinks there's only a 15% chance Omicron is more lethal than Delta
Are there other predictors? What about what are doctors seeing? Across the board, milder symptoms. Another good news!
Listen to this doctor: she's just not seeing the same level of aggressiveness. Yes!
https://twitter.com/EssexPR/status/1470007687475773449?s=20
But hold on a sec: is this because the virus is less lethal? Or because we're more immune?
As I've explained in the past, we should *not expect COVID to become less lethal over time*.
True for Alpha, true for Delta, likely true for Omicron.
As I've explained in the past, we should *not expect COVID to become less lethal over time*.
True for Alpha, true for Delta, likely true for Omicron.
https://twitter.com/tomaspueyo/status/1343868475492732928?s=20
This is due to passage: the same reason that makes a virus more transmissible tends to make it more lethal, *unless it needs to evade death to be more transmissible*. This is not the case in COVID
By the time somebody dies, he's been usually isolated for weeks. Ample time for the virus to become more aggressive and pull up the time of death without suffering in terms of contagiousness.
But if this is true, why would the virus appear less lethal? Immunity.
But if this is true, why would the virus appear less lethal? Immunity.
Immunity levels in SA and EU are very high, either through natural immunity or vaccines. Up to 80-90%.
So the virus had to evolve for immune escape, and that's what it did.
But it didn't need to evolve for lower lethality. Why would it?
So the virus had to evolve for immune escape, and that's what it did.
But it didn't need to evolve for lower lethality. Why would it?
Key takeaway: this virus
- Is likely about as transmissible as Delta
- Has more immune escape
- My guess: is probably ~as lethal for naive immune ppl, but *a bit more* lethal than Delta against immunized people
Which leads us to the Key Omicron Question:
- Is likely about as transmissible as Delta
- Has more immune escape
- My guess: is probably ~as lethal for naive immune ppl, but *a bit more* lethal than Delta against immunized people
Which leads us to the Key Omicron Question:
What's the fatality rate of Omicron vs. Delta for
-Vaccinated or previously infected?
-Unvaccinated?
Evidence➡️the most likely outcome is that Omicron is worse across both, but since vaccinated and previously infected have grown since Delta, it doesn’t appear to be the case.
-Vaccinated or previously infected?
-Unvaccinated?
Evidence➡️the most likely outcome is that Omicron is worse across both, but since vaccinated and previously infected have grown since Delta, it doesn’t appear to be the case.
This weird effect has a name: it’s Simpson’s Paradox
https://twitter.com/tomaspueyo/status/1470887288205103105?s=20
I go into much more detail about all of this in this week’s article, The Omicron Question
unchartedterritories.tomaspueyo.com/p/the-omicron-…
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