Since everyone's so read up on R0 (reproductive number) of diseases due to the #coronavirus now, thought I'd do a quick thread explaining herd immunity
Both concepts are closely related!
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The R0 of a disease is the number of new people the disease infects, on average, in a naive population (i.e. never had the disease before) For the
#nCoV19, that number is ~22 replies 2 retweets 9 likesShow this thread -
So, 2 new people infected per person who gets sick How does this relate to herd immunity? Well, herd immunity is what happens when enough people are immune to a disease that the reproduction rate (R) drops below 1
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An R below 1 means that, on average, each person infects less than one new person, so the disease eventually stops spreading Great news right?
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For different diseases, that means that you need different numbers of people vaccinated to prevent transmission The formula is pretty simple - (R0-1)/R0 = % immune required
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For the coronavirus, that would mean that (2-1)/2 = 50% of the population would need to be vaccinated to prevent spread of the disease, on average (it's not that infectious!) For measles, with an R0 of 15-18, the number is 92-95%!
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You can also reduce the effective reproduction rate, R, using other measures like quarantining sick people, which is what we're doing now
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P.S. you can also see populations reaching herd immunity if enough people catch a disease, but this has the disadvantage of lots of people getting sick which is why we vaccinate
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Oh, also if we took the R0 of 3.8 that's been the highest estimate for the coronavirus (and sprouted the infamous PANIC THERMONUCLEAR PANDEMIC tweet), the % vaccinated would have to be (3.8-1)/2.8 = 74% vaccinated to reach herd immunity
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(Above tweet should read (3.8-1)/3.8 = 74%, sorry about the typo)
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Replying to @GidMK
Great thread! Slight caveat of ‘we don’t have a vaccine for this yet though’ isn’t it?
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