CONSIDERATIONS ON HERD IMMUNITY
I'm reading a few threads showing that in most cities where 20%+ of the population got antibodies, COVID cases drops.
That's great.
However, it might not be as simple.
Some considerations in this thread (1/N).
I'm reading a few threads showing that in most cities where 20%+ of the population got antibodies, COVID cases drops.
That's great.
However, it might not be as simple.
Some considerations in this thread (1/N).
2/ First, as a disclaimer, I'm not a doctor nor an epidemiologist, and this thread asks questions rather than provide answers. I'd love anyone who studied the topic to contribute his comments, or point me to people who did address my questions.
3/ I rejoice at seeing that some cities managed to keep their number of daily new cases very low, such as the example below.
4/ However, other places such as Sicily did the same, and they did it without reaching herd immunity (2-3% of Italians showed antibodies in August; more at the North, and most probably less in the South and in Sicily). 
5/ Such regions that fared well without high antibody % have no guarantee of faring better in the future, as shown by what happened a few months later.
6/ I can think of two possible explanations for Sicily:
- They reached herd immunity in a few cities only, and new cases came from other cities.
- They are far from herd immunity, and the good results were obtained by a change of behaviors (lockdowns, masks, distancing, etc)
- They reached herd immunity in a few cities only, and new cases came from other cities.
- They are far from herd immunity, and the good results were obtained by a change of behaviors (lockdowns, masks, distancing, etc)
7/ Unfortunately, I could not find data granular enough to confirm or disprove any of the two possibilities.
8/ Another consideration is that while cases plummeted in NYC, they've been constant over the last two months or so, around 500-900 per day.
Is this compatible with herd immunity? Is it due to herd immunity being reached in some social pockets but not in others? Or…
Is this compatible with herd immunity? Is it due to herd immunity being reached in some social pockets but not in others? Or…
9/ …or is it due to the fact that new cases tomorrow depend on:
- antibodies % in a population
- behavior (social contact, masks wearing, etc)
- quantity of virus in the population
- antibodies % in a population
- behavior (social contact, masks wearing, etc)
- quantity of virus in the population
10/ For example, some evidence suggests that viral load (how much virus you inhale) might determine if and how strongly one gets infected.
Could it be for example that Sweden got it better than Italy because there was less virus in Sweden than in 🇮🇹 (so viral loads were lower)?
Could it be for example that Sweden got it better than Italy because there was less virus in Sweden than in 🇮🇹 (so viral loads were lower)?
11/ Of course, all of the above might apply.
For example, cases might decrease when 20% antibodies is reached OR when behaviors reduce the amount of virus in a town below a given density.
Or, the % of a population with antibodies to reach herd immunity can depend on viral load.
For example, cases might decrease when 20% antibodies is reached OR when behaviors reduce the amount of virus in a town below a given density.
Or, the % of a population with antibodies to reach herd immunity can depend on viral load.
12/ I do not have these answers. If anyone does, please let me know.
Either way, I believe that not all lockdowns are equal, not all distancing is equal, not all immunities are equal, not all viral load is equal, and those nuances are very, very important.
Either way, I believe that not all lockdowns are equal, not all distancing is equal, not all immunities are equal, not all viral load is equal, and those nuances are very, very important.
13/ (A clarification. In this thread, by viral load I roughly intend "how much virus you would inhale by eating in a McDonald's in that city", for example. It depends on how many people eat out, how many wear face masks, how many are symptomatic, any superspreader, etc.).
14/ I forgot to mention T cells (see below).
Most questions raised by the thread still apply though.
Most questions raised by the thread still apply though.
15/ Also, not all cases are equal.
Given a case, how much virus is he spreading?
It depends on how fast he is identified, on whether he wears face masks, on whether his town implemented social distancing, on the viral load that infected him, etc.
Many stats miss this.
Given a case, how much virus is he spreading?
It depends on how fast he is identified, on whether he wears face masks, on whether his town implemented social distancing, on the viral load that infected him, etc.
Many stats miss this.
16/ It’s a bit as if we compared two companies selling, say, apples
Only knowing how many salespeople they have is not enough to predict how many apples they will sell. What do these salespeople do? Where do they sell? How much stock they have?
Same with COVID cases & spreading
Only knowing how many salespeople they have is not enough to predict how many apples they will sell. What do these salespeople do? Where do they sell? How much stock they have?
Same with COVID cases & spreading
