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You have to ask yourself what drives exponential growth, and what eventually breaks the exponential. What drives exponential growth in an epidemic is the fact
by DiogenesKynikos 7y ago
You have to ask yourself what drives exponential growth, and what eventually breaks the exponential.
What drives exponential growth in an epidemic is the fact that each person infects some number of other people, on average. The more people are sick, the more people get infected each day. Growth is proportional to size, so you've got an exponential curve.
What stops exponential growth in an epidemic is when so many people are immune that the average sick person isn't able to infect more than one other person. At that point, the epidemic dies off exponentially.
You only reach the exponential decrease phase once a significant fraction of the population has immunity. That only happens once they've gotten sick and recovered.
Based on the transmissibility of COVID-19, it's expected to eventually infect 60% of the world population, unless a vaccine is developed before it does.
- zepolen 7y agoWoosh.
- DiogenesKynikos 7y agoYou made fun of the extrapolation of an exponential by extrapolating beyond the size of the human population. Your point was obvious, but if you meant to downplay point made by the person you were responding to, then you were wrong to do so. The exponential can indeed be extrapolated for many e-foldings, until the number of infected people is a significant fraction to the total population.
- xscott 7y agoYeah, that "can" happen. Other things "can" also happen... If you've got a real prediction, why don't you say it? And you moved the goal posts from "deaths" to "infected". I'm not a huge fan of sarcasm, but I think zepolen was right to point out that blindly predicting exponential growth is ridiculous. The world is more complicated than some sophomore level differential equations would indicate.
- DiogenesKynikos 7y agoIt's not "blindly" predicting exponential growth. Epidemics grow exponentially, for very concrete and well understood reasons. There are a number of people making fun of or playing down that fact here, which is incredibly foolish. We're facing a serious epidemic, and we ignore basic epidemiology at our own peril. > If you've got a real prediction, why don't you say it? The doubling time of the number of infected people will continue to be about three days, until strenuous social distancing measures are implemented (or in the worst case, herd immunity is reached). The rate of newly detected cases will begin to bend downwards about 1-2 weeks after the introduction of such measures, due to the delay between infection and onset of symptoms. > And you moved the goal posts from "deaths" to "infected". The number of deaths is proportional to the number of people infected.
- zepolen 7y agoThe generalization about always following an exponential increase until herd immunity is completely wrong. Proof: China's infection rate https://www.worldometers.info/coronavirus/country/china/ https://www.worldometers.info/coronavirus/country/china/
- slv77 7y agoThat is because China took drastic measures to control the spread of the virus. Many of these interventions were existing systems and cultural norms that were already in place due to the previous SARS epidemic. The US, for example, gave up on contact tracking fairly early while China had 1500 teams of at least 5 people doing contact tracking(and are still doing it) If R0 is in the range of 2-3 the interventions need to reduce transmission by 75% to 85% to get R0 values down to 0.5. At that rate exponential decay starts and the math works the same in the other direction. The China or South Korea data isn’t especially comforting when you look at the scale of interventions required to bend the curve. https://www.businessinsider.com/chinas-coronavirus-quarantines-other-countries-arent-ready-2020-3 https://www.businessinsider.com/chinas-coronavirus-quarantin...
- zepolen 7y agoYep, so the generalization is wrong.