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Comment by ramesh31 | Hacker News Reader

You need 90%+ vaccination rates to start seeing herd immunity, which is what we have for things like MMR.

It wasn’t that long ago that the scientists were suggesting 70% was sufficient. Is it that >90% is required when the vaccines don’t effectively impede transmission? Is it possible 100% would not be sufficient?

Yes it is, it depends on the efficacy of the vaccine and the transmissibility of the virus.

The 70% number was often mentioned when the original variant was still predominant end of last year. Alpha and Delta are just so much more transmissible. The vaccine was never said to prevent all infections by serious scientists

70% would have been workable for the original or 'wild type' strain. Delta and Omicron are many times more transmissible.

It's been clear for a long time that even 100% won't make the virus disappear. Yes, back in the early days when we didn't use the greek alphabet yet eradication was a reasonably possible best case outcome (though not really likely, given the transmissibility across species.

Look at how prevalent pre-delta variants are now: no, they have not disappeared because almost everybody had delta, they have disappeared because of vaccine shots combined with moderate (compared to 2020) NPI. A virus strain does not simply disappear because there's a new one in town, it keeps replicating until it runs out of hosts. And virions are certainly not defecting to a newer, more glorious flag (like humans might do)

Does a prior infected person count toward herd immunity? I have Dr. letter of my recovery.

I heard those who had it and recovered have sterilizing immunity. Is that better or worse than the vaccine non-sterilizing immunity for getting us to herd immunity?

Anecdotal, but I got my first bought of covid in Feb. 2020, and it was very flu-like for me. I've had 2 more infections after that (one, didn't even know, and the next was like a mild cold). In South Florida, we barely had a lockdown.

How do you even know it was COVID? It could have been any number of flu/cold? In feb 20 there was no way to get tested for it

The complete loss of smell and taste, was never a flu symptom to me before.

In the Denmark numbers above, only 4.3% of Omicron infections were Covid-recovered, compared to 77% being double-vax, https://news.ycombinator.com/item?id=29633285

For that to be meaningful you need to compare the per capita rate of vaccinated and prior covid infected. That’ll show you very roughly how much protection each provides in a way that’s comparable.

With hardly more than 10% recovered, total, vs almost everybody vaccinated that's not much of a difference. Very well within the range of methodical difference like in which group those recovered and vaccinated are counted and so on.

Why don’t you get the jab? It would be strictly better to have both.

Herd immunity counts nothing against delta or omicron. The endemic state, a permanent balance between immunity vaning and reinfection, that's not herd immunity. Natural immunity is just as temporary as vaccine immunity, give or take a few months.

"Natural immunity is just as temporary as vaccine immunity, give or take a few months."

Citations needed for that claim. Based on the articles below, natural immunity seems to be vastly longer lasting...

Lasting immunity found after recovery from COVID-19 https://www.nih.gov/news-events/nih-research-matters/lasting...

Had COVID? You’ll probably make antibodies for a lifetime https://www.nature.com/articles/d41586-021-01442-9

The concluding para from your Nature article says the opposite of what you're claiming, and supports the person you're replying to:

"the persistence of antibody production, whether elicited by vaccination or by infection, does not ensure long-lasting immunity to COVID-19. The ability of some emerging SARS-CoV-2 variants to blunt the protective effects of antibodies means that additional immunizations may be needed to restore levels, says Ellebedy. “My presumption is, we will need a booster.”"

Its a confusing conversation because theres different levels of immunity.

I think the bone marrow cells are indicative of long-term protection from severe illness. They have long ramp up time from the point of latest exposure.

Blood boosted antibodies will be there to thwart an infection and continue to be there to prevent reinfection but the body turns off the pump because it becomes a waste of resource without an active enemy.

So the lifecycle of a (non-boosted) person going through endemic sars-cov2 will be slow activation followed by an afterburner which will tend to get you through a wave. Or you can try to time a booster to get you through a wave without getting triggered by the actual virus.

So in a sense, there is evidence long term "slow" immunity which is less effective at preventing transmissions and so allows for waves which indicates a certain lack of immunity by another defintion. I think that leads to conflict because of fuzzy definition on either side of the conversation.

Anyway that's my mental model of this whole thing. Any glaring holes?

There is plenty of evidence of natural immunity decaying. It will likely never (not in a lifetime) fall to a level equal to an entirely unprepared immune system, but the same holds for vaccine effect: immune system responses are a log decay, with various nonlinear effects applied (thresholds, saturation, the occasional rare ADE and so on) to different aspects that are of different importance for different viruses so that the observed curves look a bit different in each case. Yes, for some viruses, even what's left after a century is enough.

But those details are completely besides the point for endemic state, endemic state is endemic state wether reinfection, on average happens every quarter or wether it happens every five years. The only difference is that anything larger than a few months will lead to massive seasonality, and longer cycles will lead to a larger severity spread. This severity spread will be the decisive factor in the question of revaccination thresholds (maybe higher than current flu shot habits, maybe lower, maybe about the same), but there are far too many uncertainties to bother with concrete predictions.

What we do know: a year or two from now there won't be any vaccine-only immunities left, everybody will either be vacc+infection or infection only.

> There is plenty of evidence of natural immunity decaying

You said something like this in another thread, but I've yet to see sources for this. Can you provide some?

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