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Comment by nabla9 | Hacker News Reader

Roughly million people live in Stockholm and 2.4 million people liven in Stockholm metropolitan area.

Assuming R0 = 2.5, you need (1-1/R0) = 60% of the population to be immune for herd immunity. That would be 600,000 in Stockholm, 1.4 million people in the metropolitan area, 6 million for Sweden.

Assuming the same infection fatality rate 0.002 as Finnish national health organization estimates: 1,200 deaths in Stockholm, 2,800 in the metropolitan area, 12,000 in Sweden. Currently there are just 1,400 total covid-19 deaths in Sweden.

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I wouldn't place too much trust in the Finnish IFR estimate. Their IFR estimate a month ago was 0.05% - 0.1%. At the time there was no data to support that, and it turns out that they had simply taken their estimates from a ten year old pandemic preparedness plan, which was designed for an influenza pandemic.

It was basically the same mistake UK did. Now they have very slowly begun to adjust away from the misleading path they originally set on.

The Finnish national health organization has been subject to severe budget cuts for the past ten years. They are still saying that masks do more harm than good, and that it's absolutely impossible to stop the virus, despite South-Korea having done so for almost 50 days already.

Once you have a certain number of infected it would take a long time (months or years) to stop it without a vaccine.

Their updated estimate is similar to ones from Iceland (mass testing) and others. More people than expected go trough the disease without symptoms. At least 50%.

The math goes as follows:

- 60% need to be infected for herd immunity.

- At least 50% of infected show no symptoms.

- CFR is 0.7%.

0.6×0.5×0.007 = 0.002

(This math assumes that everyone without symptoms is a diagnosed case, so overestimte)

> It was basically the same mistake UK did. Now they have very slowly begun to adjust away from the misleading path they originally set on.

How so?

I don't see any adjustment.

The UK strategy was to not pull the trigger on lock down too early, and then to flatten the curve in a way that fills our front line health service's capacity without overstretching it.

All while increasing numbers of beds, ventilators and distributing PPE as widely as possible.

That's broadly what's happened.

What DIDN'T happen is... well... more or less anything proactively in February. But we're certainly not alone there.

816 of the current 1400 deaths in Sweden have been in Stockholm. So based your math, we are at around 40% infection rate. I live here, and anecotely i can say that is too high. In my circles, maybe it's 10-20%. Lots of old folks homes were hit here that increase the IFR.

Reference:

https://experience.arcgis.com/experience/09f821667ce64bf7be6...

In the Netherlands with about 3.5k deaths on 17 M pop the estimation for infection rate is 3%, based on tests done on people giving blood. I'm not certain whether that 3% is an under- or overstatement (people giving blood usually more active than average, but also younger than the average inflicted and you won't go in when actively ill). It's a long stretch from a 3% to anywhere near herd protection though. The 40% infection rate for Sweden seems too high.

The 40% infection rate is an estimate for Stockholm, not for all of Sweden. The Stockholm region has less than a quarter of the Swedish population (2.3 million out of 10 million) but well over half of the covid-19 deaths (816 out of 1442). Stockholm is also the region with the lowest average age in the country, and the largest proportion of one-person households, so the fatality in the region might be skewed down.

My Norse isn't what it used to be but you're still looking at an 8x difference per capita with the Norwegian number following from a mathematical model and the Dutch number coming from inference based on blood measurements. I don't know what's true, but 40% with 816 deaths seems low. That's a mortality <0.1%.

Ask people more thoroughly. A lot of people in my circles have had vague symptoms like itchy throat or eyes, vague chest discomfort, general fatigue. I would say the 40% sounds about right.

It is estimated that at least 50% of the infected show no symptoms.

If you take that into account, it's seems my numbers are on the right ballpark again.

I like how you are using simple guesstimates to show how viable herd immunity is. Following on from this:

   600,000 people in Stockholm
   to be infected in, say, 120 days
   = 5000 new infections per day
   with, say, 1% hospitalisation
   = 50 new beds per day

This does not seem realistic to me.

50 new beds per day,

14 day average stay in hospital

50×14 = 700 extra beds.

The fatality rate depends on whether and how you can treat patients. The Finnish health care system has not yet reached capacity at this stage.

Neither has the Stockholm health care (ICU beds) reached capacity yet.

What's your point? My point was that you can't make that calculation with a current fatality rate.

Neither has the system in Stockholm, and in the rest of Sweden it barely ticks the mark.

For example in Skåne, a region with a population of 1.3 million currently 16 people are in ICU care from 6 days ago.

In Swedish: https://www.expressen.se/kvallsposten/sa-manga-ar-corona-smi...

Which fully supports the point I was making.

Do you have any links/papers that explain the Finnish estimate?

> Do you have any links/papers that explain the Finnish estimate?

Unfortunately the Finnish National Institute for Health and Welfare doesn't have a culture of being open about these things.

That herd immunity equation is really only useful in the context of vaccination when there's no active epidemic.

With an active scenario like this, it's just the point where the number of people infected per day stops going up. You still end up with like 90%+ of people getting sick before it finally peters out.

In case of influenza, you only need innumity for 30% of the population.

But it isn't influenza.

And we don’t know whether we need 60% pop. Deadly diseases tend to have lower rates.

No, we don't know for sure, but the 60+% are the current estimate based on the data available. The rates are not so much dependant on how "deadly" a disease is, but on how long you don't know you have the disease before you get noticeably sick. And there Covid-19 is so nasty. As far as we know, one is infectious for some time before (if ever) you get sick. On the other side, those who do get sick, get so badly.

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