 |
|
The definition is the same for all diseases. The
Posted on: November 9, 2021 at 23:13:10 CT
JeffB MU
Posts:
72409
Member For:
21.46 yrs
Level:
User
M.O.B. Votes:
0
herd immunity threshold varies for each disease, however. It is based upon the effective reproduction number of the virus or bacteria. R0 (R nought) is how many people an infected person would infect on average in a population with zero immunity to the disease.
Covid had an estimated R nought of between 2 and 2.5. In other words a person who contracted covid when it was first released into the world would on average infect two to three other persons. It would spread exponentially. One person would infect 2 who would infect 4 more who would infect 8 etc.
But over time as more and more people became infected and then recovered immunity began to develop in populations. Eventually the rate of spread would slow because some of the people who were exposed to the virus now had immunity and did not become infected again. This reduced the "effective R value" below the original (R nought) to some lower number. The herd immunity threshold is when the effective R value drops below 1. If it dropped to .99 for instance it would mean that on average 100 infected people would infect 99 other people. That would also mean that the number of infected people at any given time would be going down as well. Of course, over time the effective R value should also continue to drop as more and more people are developing natural immunity... or are being vaccinated if the vaccine provides some immunity.
Of course things are complicated if a virus mutates to reduce immunity or to increase or decrease the effective R value. Unfortunately, man made viruses, like Covid-19 are susceptible to more rapid mutations than naturally occurring viruses.
In any event, there is a simple math formula that can be used to calculate the herd immunity threshold:
Maths in a minute: "R nought" and herd immunity
https://plus.maths.org/content/maths-minute-r0-and-herd-immunity
Edited by JeffB at 23:14:23 on 11/09/21
Covid had an estimated R nought of between 2 and 2.5. In other words a person who contracted covid when it was first released into the world would on average infect two to three other persons. It would spread exponentially. One person would infect 2 who would infect 4 more who would infect 8 etc.
But over time as more and more people became infected and then recovered immunity began to develop in populations. Eventually the rate of spread would slow because some of the people who were exposed to the virus now had immunity and did not become infected again. This reduced the "effective R value" below the original (R nought) to some lower number. The herd immunity threshold is when the effective R value drops below 1. If it dropped to .99 for instance it would mean that on average 100 infected people would infect 99 other people. That would also mean that the number of infected people at any given time would be going down as well. Of course, over time the effective R value should also continue to drop as more and more people are developing natural immunity... or are being vaccinated if the vaccine provides some immunity.
Of course things are complicated if a virus mutates to reduce immunity or to increase or decrease the effective R value. Unfortunately, man made viruses, like Covid-19 are susceptible to more rapid mutations than naturally occurring viruses.
In any event, there is a simple math formula that can be used to calculate the herd immunity threshold:
Maths in a minute: "R nought" and herd immunity
https://plus.maths.org/content/maths-minute-r0-and-herd-immunity
Edited by JeffB at 23:14:23 on 11/09/21
Please explain why this message is being reported.
MESSAGE THREAD
The definition is the same for all diseases. The - JeffB MU - 11/9 23:13:10