> In addition to [reproduction number] R, scientists use a value called the dispersion factor (k), which describes how much a disease clusters. The lower k is, the more transmission comes from a small number of people.
SARS (2005): k ~= 0.16
MERS (2012): k ~= 0.25
Spanish Flu (1918): k ~= 1
Estimates of k for Covid-19 vary:
- An earlier study in Hong Kong said k was slightly higher than for SARS or MERS.
- Recent study [1] based on data outside China puts k ~= 0.1, which would mean 10% cases lead to 80% of the spread.
- Lower k would explain why the virus didn't spread all around the world immediately, and why many infection clusters seem to clear on their own.
Large infection clusters are thought to appear due to aerosol transmission, in particular indoors, where the risk is 19 times higher according to another study [2].
One of the fascinating and tragic aspects of tropical medicine that the current pandemic has illuminated is that understanding of emerging diseases is largely observational, incremental, and slow. The observational aspect in particular is mostly accidental and relies on either getting lucky enough to observe something or having a large enough pool of cases to look at. We literally cannot say anything with certainty about the course of the disease on a time scale longer than a year.
Does the disease produce immunity and how long might it last? Well, only as long as we have been able to observe a patent who has recovered. So, 6-7 months?
What are potential chronic complications that can result from the disease? We have little clue, because literally no one on Earth has had more than 6-7 months of medical history with this disease.
Just because we don’t have direct evidence, doesn’t mean we don’t know anything. We can make educated guesses and talk about what is more or less likely. For example, it’s less likely that immunity will last for 7 months, its more likely to last for a few years. For the majority of people who catch the virus and have a mild response to it, it’s unlikely they will have long term negative health consequences. Just because we don’t have concrete proof yet, doesn’t mean that all possibilities are equally likely to happen.
5 comments
[ 3.2 ms ] story [ 17.3 ms ] threadSARS (2005): k ~= 0.16
MERS (2012): k ~= 0.25
Spanish Flu (1918): k ~= 1
Estimates of k for Covid-19 vary:
- An earlier study in Hong Kong said k was slightly higher than for SARS or MERS.
- Recent study [1] based on data outside China puts k ~= 0.1, which would mean 10% cases lead to 80% of the spread.
- Lower k would explain why the virus didn't spread all around the world immediately, and why many infection clusters seem to clear on their own.
Large infection clusters are thought to appear due to aerosol transmission, in particular indoors, where the risk is 19 times higher according to another study [2].
1. https://wellcomeopenresearch.org/articles/5-67 2. https://www.medrxiv.org/content/10.1101/2020.02.28.20029272v...
It does make sense that the virus is more effective in a dank, windless environment, much like the environments in which horseshoe bats roost.
Does the disease produce immunity and how long might it last? Well, only as long as we have been able to observe a patent who has recovered. So, 6-7 months?
What are potential chronic complications that can result from the disease? We have little clue, because literally no one on Earth has had more than 6-7 months of medical history with this disease.