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Comment by StavrosK | Hacker News Reader

Why would it? Everyone is trying to avoid getting infected (and dying). Isn't that what we should do?

Herd immunity means "it's killed as many people as it could".

Yes and no. the theory behind flattening the curve is to try and plateau the infection rates so that hospitals do not become overwhelmed.

If we are going to be in a situation where hospitals have ample capacity, and we figure out a way to combat the symptoms of covid-19 without loss of life, then social distancing restrictions would be lifted immediately.

"Flattening the curve" is different from "herd immunity", though. You can have herd immunity without flattening the curve.

I for one don’t fancy playing the Russian roulette even if hospitals have ample capacity and world class treatment, so I will distance myself the hell away and protect myself the best I could when I have to face people until this whole thing is over.

No, herd immunity means "enough people are resistant so the vulnerable ones don't get infection spread to them at all". There's a big difference there.

How would you be resistant without getting infected? There's no vaccine.

because there is enough people who are resistant in the population that virus can no longer spread

I thought herd immunity required >90% of people to be resistant, but I guess that's only true for very contagious stuff like measles. According to https://en.wikipedia.org/wiki/Herd_immunity#Mechanics COVID-19 might only need 30% of the population to be resistant if it has an R0 of 1.4, or 75% if the R0 is 3.9. It's still a good chunk of the population but it's a lot different than I thought.

If the propagation of a virus is similar to a fire running through a population, herd immunity is analogous to a backfire.

If most of the people are immune, the fire has no combustible to propagate and it stops.

The level at which this happens depends on the ease at which the virus spreads. If it spreads easily, herd immunity kicks in much later than in the reverse case.

You wouldn't be, you'd just be relatively unlikely to be infected since most people around you would be immune and the virus would have difficulty getting to you.

But the degree and duration of immunity that usually follows SARS-nCoV-2 infection isn't well established yet, and coronaviruses in general are noted for not producing lasting immunity.

Yeah that's what I'm asking. By the time you get to "herd immunity", most of the population has already been infected. To get most people to be resistant, most people need to get sick first!

Right, enough people are resistant because they already got infected. I don't see how that's different from what I said.

It's different because when you go for herd immunity you would try to infect low-risk groups first so the high risk groups would never get it at all. This would result in an overall minimal death rate, could be a tenth or less of the death rate if the infections were evenly distributed.

Second that. I would write it differently:

Enough people are resistant so instead of becoming virus factories and spread it further they stop the infection with their immune system.

No, it means that "enough people have been infected that each new infection causes less than 1 infection." Lets say we're in the middle of an outbreak and reach herd immunity. The infected people are still going to infect others, just less than the number currently infected. And then those people go on to infect an even smaller number. And so on. This is called "overshoot" and can end up being a significant number of people. One of the reasons for the "flatten the curve" heard immunity strategy is that it limits overshoot as well as reducing strain on medical facilities.

I see, thanks for the clarification.

Technically herd immunity occurs when R=1, people will continue to be infected after that.

https://en.wikipedia.org/wiki/Herd_immunity#Mechanics

> Isn't that what we should do?

It depends on the costs of doing so.

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