Flatlander et al
I would not worry overly about the exact definitions. Some diseases are truly air-borne, like Measles, and can be transmitted over long distances. Flu and COVID are not but are carried in droplets of various sizes. The larger ones dropping to the ground almost immediately while the smallest may behave almost like air-borne. Flu produces a lot of mucus in the nose and upper respiratory tract (URT) which is explosively expelled by coughs and sneezes projecting a large droplet cloud of mixed sizes (hence the recommendation to catch as much as you can in a mask, tissue, elbow, scarf etc.). In COVID the disease is concentrated in the lower lung (LRT) but does not bind as well to the cells in the URT. This produces a dryer cough, and hopefully less of a droplet cloud. It may also create a different distribution of droplet sizes and there has been some speculation that this is resulting in more smaller droplets and so the 'safe distance' in meters of separation may need to be a bit larger. Droplets can be inhaled directly or fall on a surface and then cause infection by fomite transmission. Apart from the natural coughing transmission droplets may be generated by medical procedures that do not necessarily mimic the coughing size distribution and if a lot of small droplets are produced additional PPE and increased separation distances may be required. Regardless of the mix a radius around the infectious individual will be dangerous and the closer you are the greater the risk. For flu most droplets fall within 2m which is the general separation recommendation. If COVID is producing more of the very small nuclear droplets you may need to increase this a bit to achieve the same diminution of risk. Note 2m or 3m is not zero risk just much lower.
Another way to think about social distancing is in terms of the reproductive number (R0). If a disease has an R0 of 2 then if you halve the number of times you put yourself at risk you reduce it to 1. Get it below one and the disease will die out. This is not difficult for most people go to the shops half as often, see half as many people at work, stay twice as far away, avoid crowds and wear gloves and a scarf. I think social distancing every flu season anyway so it is not really a change for me.
I would not worry overly about the exact definitions. Some diseases are truly air-borne, like Measles, and can be transmitted over long distances. Flu and COVID are not but are carried in droplets of various sizes. The larger ones dropping to the ground almost immediately while the smallest may behave almost like air-borne. Flu produces a lot of mucus in the nose and upper respiratory tract (URT) which is explosively expelled by coughs and sneezes projecting a large droplet cloud of mixed sizes (hence the recommendation to catch as much as you can in a mask, tissue, elbow, scarf etc.). In COVID the disease is concentrated in the lower lung (LRT) but does not bind as well to the cells in the URT. This produces a dryer cough, and hopefully less of a droplet cloud. It may also create a different distribution of droplet sizes and there has been some speculation that this is resulting in more smaller droplets and so the 'safe distance' in meters of separation may need to be a bit larger. Droplets can be inhaled directly or fall on a surface and then cause infection by fomite transmission. Apart from the natural coughing transmission droplets may be generated by medical procedures that do not necessarily mimic the coughing size distribution and if a lot of small droplets are produced additional PPE and increased separation distances may be required. Regardless of the mix a radius around the infectious individual will be dangerous and the closer you are the greater the risk. For flu most droplets fall within 2m which is the general separation recommendation. If COVID is producing more of the very small nuclear droplets you may need to increase this a bit to achieve the same diminution of risk. Note 2m or 3m is not zero risk just much lower.
Another way to think about social distancing is in terms of the reproductive number (R0). If a disease has an R0 of 2 then if you halve the number of times you put yourself at risk you reduce it to 1. Get it below one and the disease will die out. This is not difficult for most people go to the shops half as often, see half as many people at work, stay twice as far away, avoid crowds and wear gloves and a scarf. I think social distancing every flu season anyway so it is not really a change for me.
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