Comment by nabla9 | Hacker News Reader

Comment by nabla9 | Hacker News Reader

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Here:

1) Exposure to influenza virus aerosols during routine patient care. https://academic.oup.com/jid/article/207/7/1037/2192312

>HCPs within 1.829 m of patients with influenza could be exposed to infectious doses of influenza virus, primarily in small-particle aerosols.

2) Short-range airborne transmission of expiratory droplets between two people. https://www.ncbi.nlm.nih.gov/pubmed/27287598

>The threshold distance of about 1.5 m distinguishes the two basic transmission processes of droplets and droplet nuclei, that is, short-range modes and the long-range airborne route.

It seems that depending on conditions < 2m is a good practical threshold for droplet transmission. Probably more if person is really sick.

The goal is to get as small dose viruses at once as possible. Immune system can usually fight off small exposure.

Sometimes even healthy people who inhale huge amount of viruses into their lungs at at once can get very seriously sick because their immune system struggles with the large sudden attack and goes into overdrive.

> 1) Exposure to influenza virus aerosols during routine patient care. https://academic.oup.com/jid/article/207/7/1037/2192312

A relevant graph is https://academic.oup.com/view-large/figure/90149845/jis77302...

This shows that large droplets don’t travel, but that small (< 4.7nm - accurate?) do travel e.g. ~10% particles measured at 6 feet.

Issue 1: drop off rates look to rude approximation to be r^2. The were measuring a point source. If you are standing in a line of people, you need to integrate along the line, and inter-person distance needs to be increased. A field of people (supermarket) needs something different...

Issue 2: large droplets should travel further if outdoors? (turbulent air)

Issue 3: cigarette smoke is a familiar visual indicator: “cigarette smoke particle mainly distributed in the size range 0.1 to 1.0 micron”. Think about how the smoke exhaled by someone travels (ignore how smoke travels from end of cigarette due to heated air).

1.829m sounds like it was converted from exactly 6 feet.

No it’s 6.0006 feet. Obviously.

>The goal is to get as small dose viruses at once as possible. Immune system can usually fight off small exposure.

This is interesting, i had always thought it was binary, either you get infected or you don't

Nope. The higher the dose you get at any given time, the likelier it is that enough virions will establish footholds in enough cells to overwhelm the local protective response and survive to replicate.

To be clear, that's not an antibody-mediated immune response, which takes longer. Before then, cells penetrated by virus particles often undergo apoptosis, self-destructing to defend the larger organism by preventing the virus from hijacking the cell's machinery to reproduce itself. Sometimes the virus wins, though. So the more particles you're exposed to, the higher the odds that one or more will establish itself and start making you sick.

For more, see e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2517702/ - but if you don't want that level of detail, you can just think of it as "flattening the curve" on an individual scale, and not really go far wrong.

edit: More accurate use of "immune" now that I'm not commenting from a phone with a small screen. Apoptosis isn't initiated by the immune system, but rather within the affected cell itself, and doesn't only occur in response to viral invasion; many types of cellular injury or damage can cause it, including most of the ways that a cell can become precancerous. (Which happens a lot more often than you might think! But most such cells self-destruct before they can give rise to a tumor.)

> This is interesting, i had always thought it was binary, either you get infected or you don't

IIRC, some vaccines work by exposing the person to a tiny amount of virus so that their immune system can "learn" how to fight that particular type of virus.

Do we have any idea how this changes outdoors? I could see it being worse because the wind spreads virus farther or better because it gets diluted quicker.

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