This would be consistent with Omicron having certain immune-escape features. People who previously had strong, neutralizing immunity (from vaccination or prior infection) may experience reinfection/breakthrough infection, but because of T-cell immunity or residual antibody immunity the variant is less likely to cause severe disease than it would in a non-immune person.
If the above hypothesis is true, that doesn't necessarily make Omicron "milder" than Delta. Omicron would be infecting people who would not be infected by Delta, so in those people (some disease) is more severe than (no disease). I have not yet seen evidence one way or the other regarding severity for a first infection in a non-immune person.
That is to say, "Omicron is milder!" could be an artifact of Simpson's Paradox.
What confuses me about these reports is that the relevant South African districts report ~25% vaccination rates; so it sounds unlikely that the mildness observed is due to previous immunity. Or is the assumption that most of these people have had COVID before?
As it turns out that’s a myth. AIDS, rabies, measles, Ebola, Marburg, Hep A/B/C: none of these viruses have gotten milder, in 60+ years of evolution. There are Egyptian mummies showing signs of smallpox, a disease that killed 350,000,000 people in the 20th century, more than two millennia later.
It’s also quite obvious, mechanistically: COVID doesn’t lose many infections by eventually killing the patient who, by then, is obviously sick and most often in the hospital. It gets 80%+ of retransmission even before symptoms appear, removing all evolutionary pressure from the later stages.
> It’s also quite obvious, mechanistically: COVID doesn’t lose many infections by eventually killing the patient who, by then, is obviously sick and most often in the hospital.
But viruses spread in the real world not some hypothetical lab. In the real world as viruses become deadlier they tend to provoke a much larger response from governments and populations, both in terms of prevention and vaccines/cures/treatments. That's why there's a lot more money spent on potential HIV vaccines than on vaccines for the common cold. Being deadlier is a distinct disadvantage if you're a virus trying to survive for the long haul.
So how does Omicron have any advantage, right now, from that supposed difference? Wouldn’t every mild strain just suffer from governments’ efforts targeting the bad strains, which ruin it for all the others? Note that any future benefits cannot explain evolutionary changes in the present because viruses don’t strategize.
No, deadliness doesn't really matter. What matters is how many people in infected person can infect before symptoms become too severe. Covid has a rather long period where patients are infectious while showing no symptoms at all, so it's already very good at that game.
It depends on whether you consider vaccines and human intervention as part of the 'natural' feedback process that tends to make viruses less severe.
In other words, the high-level theory is that more severe viruses either kill their hosts, or make them so sick that they stop interacting with other potential hosts. A form of social distancing, if you will.
In both cases, the virus is triggering some form of behavior change in its host that reduces its reproduction, providing evolutionary pressure towards milder viruses.
One could argue that the development and wide distribution of a vaccine is just one form of host behavior change, and should be factored in.
And the reason we pursued vaccination rigorously enough to eradicate it was because as you say it is very deadly and very contagious.
Something with a mortality rate of 30+% and kills children at orders of magnitude higher rate than COVID has is far easier to convince the world populace to vaccinate for than something with 1-2 order of magnitude lower CFR.
So you can most 100%, certainly say, it was eradicated because it is so deadly. If only say 0.5% of people died from it, disproportionately the elderly those with comorbidities, eradicating smallpox would have been a hell of a lot harder to get worldwide vaccinations on board. A hell of a lot.
No. The transition you're talking about is a general tendency in viruses, not some kind of rule. SARS-CoV-2 seems to avoid it, in fact, due to its tendency to spread before people even have symptoms.
It's honestly too early to tell what the characteristics of Omicron are, there's just not enough data. Some anecdotes look positive, but mostly what we're seeing is the media going nuts trying to say something when the responsible thing to do is say nothing and wait.
Well, there is not enough data for _simple_ answers yet (and people like simple, so the media likes simple; scientists also like simple).
But there is a lot of data, it is just hard to interpret, even for experts (which I'm not): It is currently summer in South Africa, but there was a summer wave last year. "Around 60-70% of South Africans have already had a Covid-19 infection" (from another comment). Age distribution. How fast omicron is spreading and why. How many are vaccinated (once, twice,...). How many breakthrough infections. Delta and other variants are spreading faster than the previous mostly due to higher viral load. Omicron seems to have has higher viral load. Omicron also binds to ACE2. What is the typical delay between infection and hospital / ICU admission. Some of this is discussed e.g. in https://yourlocalepidemiologist.substack.com/p/omicron-were-...
I understand that the media doesn't just stay silent. What I'm missing from them is in-depth and up-to-date info, with error bars. They can do that for weather forecasts, they should also be able to do this for omicron.
How does one jump from "Omicron is more transmissible and less deadly than Delta" to "Immunity...is kicking in!" That seems like quite a leap compared to a seemingly much more likely reason, that this is a mutation and it just happens to be less deadly (probably because of whatever change makes it more transmissible but still basically random chance/evolutionary pressure). I don't see how previous infections and/or vaccinations have anything to do with the characteristics of Omicron.
If mutation increases chance of vaccinated person getting a detectable infection, the hospitalization stats may show lower rates even though it is no less severe for the unvaccinated population.
> (probably because of whatever change makes it more transmissible but still basically random chance/evolutionary pressure)
That's the trick. Delta already appears to be very, very transmissible. If Omicron's growth is due entirely to improved transmissibility, then it would have to spread in a non-distanced, vulnerable population at an implausibly high rate, comparable to some of the most transmissible viruses ever studied.
However, if Omicron's improved spread is partially through immune escape, then its growth could be explained through reinfections and breakthrough infections -- people who are largely immune to Delta are contracting a mild case of Omicron. That does not make the variant inherently less deadly, since it's not an apples-to-apples comparison on the ill populations.
It will probably be some time yet before we have reliable statistics on the severity of Omicron in the never-infected, never-vaccinated cohort. In the meantime, there's reasonable cause to be concerned for vulnerable people (elderly, people with lung conditions, or the immunocompromised) who are partially relying on low community infection rates for their personal protection.
>Immunity through vaccination and previous infection is kicking in!
Because this version is more transmissible, and (theoretically?) causes your body to create antibodies that are effective against the other variants, this version of the virus will cause more people than ever to have antibodies without as much risk of death or long-term illness. People will either get the vaccine, or their risk of contracting covid will go up.
They didn't mean "has kicked in", they mean it's starting to.
That seems like a rather premature conclusion. WHO mentioned:
> Data which looked at hospitalizations across South Africa between 14 November and 4 December found that ICU occupancy was only 6.3 % – which is very low compared with the same period when the country was facing the peak linked to the Delta variant in July.
Did they account for previous infection or vaccination status? What if a lot of these are breakthroughs/reinfections. Considering excess deaths in South Africa, their national data on number of cases is sort of, doubtful [1].
Further, they seem to have observed mainly a population under 40.
Vaccination rate in SA is high for Africa but still low - was 35% in late November. Unlike much of the rest of Africa they're not limited by vaccine supply and have asked vaccine makers to slow shipments as they have enough in stock at the moment:
So a random twitter thread from some random twitter user? How about post tweets from epidemiologists who study the thing.
Right now there is a big dichotomy. The majority of the epidemiologists and scientists say things are going to be bad. Then we have mainstream media going off of clinical notes. Still those notes don't square with increased hospitalizations of the very young.
We are probably right in the middle of Simpson's paradox and only time will tell.
Having a bit of cognitive dissonance to find out that experienced vaccine researchers are furries?
The poster's bio on the right clearly states that they're a senior vaccine R&D scientist, and they've been posting well-sourced and cogent analysis of the pandemic since it started. This isn't just some rando on Twitter.
It's literally too early to answer that question. The proxies at this point are basically linearly related -> case counts, hospitalizations, ICU, death.
It took months to answer that for Delta vs the reference... And everyone said Delta was less lethal than the original strain and surprise it is not.
That would require being aware of "immunity" in the population being compared, with order of least to most being something like: unvaccinated without previous infection, previous infection, vaccinated, and vaccinated with breakthrough infection/previous infection with vaccine.
If you just looked at something raw like hospitalization/infected, like I see being used, you don't get a meaningful comparison, since much of the population now has some form of immunity compared to delta.
The most interesting would be comparing hospitalization/infected for unvaccinated at some older age, like > 50yo.
I don't disagree entirely. I mainly think it's stupid. Flight bans haven't worked in March 2020, nor December 2021 ("UK variant"), and there's no reason to believe they would work now. The only thing that seems to work (to some degree) is AUS/NZ/SG-style total flight ban.
But then the purpose of politics is showmanship, not effective action.
If the above hypothesis is true, that doesn't necessarily make Omicron "milder" than Delta. Omicron would be infecting people who would not be infected by Delta, so in those people (some disease) is more severe than (no disease). I have not yet seen evidence one way or the other regarding severity for a first infection in a non-immune person.
That is to say, "Omicron is milder!" could be an artifact of Simpson's Paradox.