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Thread: Disease and pandemics thread (because it's science)

  1. #2431
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    Johnson & Johnson vaccine is temporarily suspended while they investigate an illness. We’ve already learned that such pauses are not uncommon.

    Meanwhile, the AstraZeneca trial in the US remains on hold while an FDA review continues.
    I may have many faults, but being wrong ain't one of them. - Jimmy Hoffa

  2. #2432
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    Quote Originally Posted by Copernicus View Post
    Now the CDC is revising their guidelines. https://www.yahoo.com/news/cdc-says-...034950288.html
    Quote Originally Posted by Van Rijn View Post
    And now they reverted it, saying it was posted in error, but apparently are planning on making some change in guidelines.
    Perhaps worth pointing out that this settled down a couple of weeks ago. The CDC's How Coronavirus Spreads page has an accompanying Scientific Brief about aerosol transmission which says, among other things:
    Diseases that are spread efficiently through airborne transmission tend to have high attack rates because they can quickly reach and infect many people in a short period of time. We know that a significant proportion of SARS-CoV-2 infections (estimated 40-45%) occur without symptoms and that infection can be spread by people showing no symptoms. Thus, were SARS-CoV-2 spread primarily through airborne transmission like measles, experts would expect to have observed considerably more rapid global spread of infection in early 2020 and higher percentages of prior infection measured by serosurveys. Available data indicate that SARS-CoV-2 has spread more like most other common respiratory viruses, primarily through respiratory droplet transmission within a short range (e.g., less than six feet). There is no evidence of efficient spread (i.e., routine, rapid spread) to people far away or who enter a space hours after an infectious person was there.
    In other words, the real-world epidemiology says aerosol transmission is rare, despite all the concerns raised by laboratory and simulation studies (and the various allegedly "epidemiological" studies performed by non-epidemiologists).

    This is something I've already pointed out more than once on this thread, whenever the aerosol spectre has raised its head. I'd just like to say that I in no way pressurized the CDC to fall into line with my views.

    Grant Hutchison

  3. #2433
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    https://www.pnas.org/content/117/22/11875
    Droplets, speech droplets and their Virion load. The authors point out that largish 50 micron droplets might hang around by getting smaller, due to evaporation, and can carry virions to anyone nearby. So it’s not just avoiding people by distance, it’s keeping quiet! Any front row of the stalls playgoer will recognise the gentle rain of spittle as the actors perform their stuff. No wonder social gatherings are discouraged. It does seem to make it clear how vulnerable people should protect themselves and has been clear all along, from past experience of epidemics.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  4. #2434
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    Quote Originally Posted by profloater View Post
    https://www.pnas.org/content/117/22/11875
    Droplets, speech droplets and their Virion load. The authors point out that largish 50 micron droplets might hang around by getting smaller, due to evaporation, and can carry virions to anyone nearby.
    There was a fairly robust critique of that study in the Lancet, questioning its generalizability to the real world.
    First, the main assumption in the model is that dehydration is key to reducing the diameter of the expelled droplets, allowing droplets to become aerosols. The experiment was done in an environment with a relative humidity of 27%, which is below the minimum recommended indoor relative humidity of 40%. Second, the authors assumed an average viral load in saliva of 7 × 106 copies per mL on the basis of a prospective study wherein viral load was measured in sputum. Thus, they assume that viral load in sputum is the same as in saliva. The group also assume that every RNA copy detected is a potentially infectious virion, without acknowledging that in the cited study samples containing fewer than 106 copies per mL never resulted in a viable virus being isolated. An additional required proof would be to show that the viable virus is infectious and that the load is higher than the infectious dose.
    (Many more reservations are expressed in the article, but the two above are the highlights.)

    The authors then made an attempt at a rebuttal, but I don't find it compelling.

    Grant Hutchison

  5. #2435
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    Quote Originally Posted by grant hutchison View Post
    There was a fairly robust critique of that study in the Lancet, questioning its generalizability to the real world.(Many more reservations are expressed in the article, but the two above are the highlights.)

    The authors then made an attempt at a rebuttal, but I don't find it compelling.

    Grant Hutchison
    Thanks but while aerosols are not highly effective, surely droplets are? That is the reason for masks and two metres and avoiding social contact indoors. I did not pick up that the authors suggested conversion to aerosol, only that droplets got smaller and thus fall more slowly.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  6. #2436
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    Quote Originally Posted by profloater View Post
    Thanks but while aerosols are not highly effective, surely droplets are? That is the reason for masks and two metres and avoiding social contact indoors. I did not pick up that the authors suggested conversion to aerosol, only that droplets got smaller and thus fall more slowly.
    The aerosol conversion is implicit in the abstract:
    Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per second. In a closed, stagnant air environment, they disappear from the window of view with time constants in the range of 8 to 14 min, which corresponds to droplet nuclei of ca. 4 μm diameter, or 12- to 21-μm droplets prior to dehydration.
    (My bold.) Of course it's a continuum, but for the purposes of discussing respiratory virus transmission, the cut-off between "aerosol" and "droplet" is usually drawn at 5μm. Basically, the Lancet critique is saying that the experimental conditions that led to the 8- to 14-minute persistence do not adequately simulate what happens to speech droplets in the real world.
    So the critique is very much supporting the idea that distancing is our main line of defence, and that in most enviroments we're actually not going to end up walking through an aerosol mist of infective droplets left by someone who went by ten minutes previously, speaking loudly.

    Grant Hutchison

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