7/ So let's consider what would be required for R to drop below 1 in this context R0 = 3 If 10% of the population is immune to COVID-19, this will be reduced to R = 3*(1-0.1) = 2.7 The disease still spreads
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8/ Luckily, this is just maths, so we can work it out We want R to be below 1 This makes it into a simple equation: R<1
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9/ Substituting in for R, we get: R<1 => R0*(% susceptible)<1 => %susceptible<1/R0 Solving for R0 = 3, we get %susceptible<33.3% In other words, as long as more than 33% of the population is susceptible, the disease spreads
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10/ To put it another way, we need 67% (2/3) of the population to be IMMUNE to the disease for it to stop spreading This is what's known as the HERD IMMUNITY THRESHOLD
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Health Nerd Retweeted Health Nerd
11/ But that brings us back to this earlier point The only way, currently, to be immune to the disease is to GET SICK and then GET BETTERhttps://twitter.com/GidMK/status/1247328596890275840?s=20 …
Health Nerd added,
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12/ So what we're really saying is that, for the herd immunity threshold to be reached, ~67% OF THE POPULATION has to be infected That is a HUGE problem
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13/ How much of a problem? Well, assuming a relatively generous infection-fatality rate of 0.3%, if 67% of Australians get infected with
#COVID19 then ~50,000 people die A high price to pay indeed2 replies 1 retweet 13 likesShow this thread -
14/ Taking more realistic estimates of the fatality rate, we might see 100,000 or more people die before reaching this point Most would, I think, regard that as the most abject of failures
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15/ By definition, herd immunity is not and can never be a solution to
#COVID19, unless we are comfortable with a staggering death toll fin5 replies 5 retweets 33 likesShow this thread -
Replying to @GidMK
Bit isn't the R0 highly dependent upon social measures. E.g. if we're all out at the beach together the R0 will be higher, if we all social distance properly the R0 will be lower? If that's the case how does one calculate an R0 given how dynamic our social measures are?
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Nope. R0 is about the disease when no measures are in place and no one is immune. R is the one that changes
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