A more useful definition, however, is that herd immunity is the point at which enough people are immune to a disease to prevent non-immune people from getting itpic.twitter.com/px8N5xxZU1
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
Based on the table above, what's the R for measles in a population with 75% vaccination rates?
Here's a more difficult question - based on the equation for R, what is the formula to work out the % for herd immunity (HI)?
This is more complex because you have to think about what herd immunity really means Herd immunity means that each person passes on the disease to fewer than 1 person (on average), so the disease eventually peters out
What this means, in technical terms, is that R<1 I.e. the effective reproduction rate in the population is less than 1
Mathematically, this gives us the minimum threshold for herd immunity as: R0*(1-HI) = 1 Where R = 1 and R0 is calculated based on the disease Turning this around, we get: HI =1-(1/RO)
So to work out the threshold for herd immunity, we just have to solve this for each disease! Pretty cool, huh?
What's the herd immunity threshold for mumps, based on this formula?
Completing the formula, we get: HI = 1-(1/4) to 1-(1/7) = .75-.86 = 75-86%
What this means is that we have to vaccinate 75-86% of the population to reach the threshold for herd immunity for mumps
The more infectious the disease, the more you have to vaccinate Measles can live for hours, even days, outside the body, and has an R0 of >12, which means that we need to vaccinate 95% of the population to be sure it won't spread
Smallpox only has an R0 of 7, which means that we only had to vaccinate ~85% of people to eliminate the disease
And that's it. That's how herd immunity works Simple, easy, incredibly, wonderfully powerfulpic.twitter.com/GywhQILLPQ
People do still get these diseases. No vaccine is 100% effective - although many are close to that - so vaccination rates often have to be higher than even the theoretical herd immunity threshold
There are also a lot of people who have been scared away from vaccination by anti-vaccine activists who spread fear about lifesaving medical interventions #VaccinesWork
But we know that vaccinations WORK
Australia has now eliminated endemic measles and rubella, and almost entirely eliminated many other infectious diseases, with some of the highest vaccination rates in the world #VaccinesWorkpic.twitter.com/MdFUNBp6U7
So get your vaccines
They will not only stop YOU from getting sick, they'll also stop you from passing diseases onto more vulnerable people like babies and immunocompromised people #VaccinesWork
And the next time someone says "herd immunity is a myth!", feel free to reference this thread and/or blog Herd immunity is simple maths, nothing more, nothing less
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.