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In order to get infected you need to get exposed to an infectious dose of the virus; based on infectious dose studies with MERS and SARS, it is estimated that a
by nkurz 6y ago
In order to get infected you need to get exposed to an infectious dose of the virus; based on infectious dose studies with MERS and SARS, it is estimated that as few as 1000 SARS-CoV2 viral particles are needed for an infection to take hold.
As far as I know, this statement is somewhere between "completely wrong" and "very misleading". There is no minimum number of viral particles necessary for infection. Rather, there is a curve of probability of infection depending on the number of viral particles. Going by the definition in the link[1] the author provides, "The minimal infective dose is defined as the lowest number of viral particles that cause an infection in 50% of individuals (or ‘the average person’)."
Which is to say that there is no dose that is "safe", only doses that are less likely to cause an infection. Very brief exposures to 100 contagious people is just as likely to cause infection as a 100x exposure to one. Chance of infection is not a linear function of number of viral particles (since one can't be infected more than once) but can be approximated as linear at low numbers of particles. I feel like this makes most of the rest of the article moot.
Am I wrong? Is the risk of infection actually sublinear below some threshold dose? Is there thus some "safe" exposure time that can be relied on? Or is the article as wrong/misleading with regard to the risks to an individual as it seems?
[1] https://www.sciencemediacentre.org/expert-reaction-to-questions-about-covid-19-and-viral-load/ https://www.sciencemediacentre.org/expert-reaction-to-questi...
- londons_explore 6y agoI believe the theory is that if a virus multiplies with some exponential rate, say doubling every 6 hours, and the immune system takes some fixed time to respond, say 5 days, then the highest virus population in a person is directly proportional to the starting dose. Obviously the above is highly simplified, but are a model which would explain any sublinear effects, if they exist.
- nkurz 6y agoThis is a good point, and would explain how there could be a threshold effect on initial dosage. On the bright side, if this is true, it would make inoculation against the disease fairly easy: give a measured light dose, and reliably generate a mild case. On the not-so-bright side, while it is a theory, I don't think it is anywhere near proven. If you've come across it, I'd love to see more evidence that this theory is true. I'm starting to double down on my "just plain wrong" interpretation. The author of this article says repeatedly that one can be safe by simply avoiding extended exposure: "Again, assuming every virus is inhaled, it would take ~5 minutes of speaking face-to-face to receive the required dose." "In these situations there is not enough time to achieve the infectious viral load when you are standing 6 feet apart or where wind and the infinite outdoor space for viral dilution reduces viral load." "You would have to be in their airstream for 5+ minutes for a chance of infection." I think this article is full of bad, dangerous, and unproven advice. I think the author has confused population level statistical risk (where reduced exposure can reduce R0 below 1 thus preventing epidemic spread) with personal risk (where exposure to a deadly disease can be deadly).
- FabHK 6y ago> give a measured light dose, and reliably generate a mild case. That’s how it used to be done, eg for smallpox. Inoculation or variolation: https://en.m.wikipedia.org/wiki/Variolation https://en.m.wikipedia.org/wiki/Variolation