starlightomatic:

we-are-star-stuff:

Herd immunity is the idea that if enough people get immunized against a disease, they’ll create protection for even those who aren’t vaccinated. This is important to protect those who can’t get vaccinated, like immunocompromised children. 

You can see in the image how low levels of vaccination lead to everyone getting infected. Medium levels slow down the progression of the illness, but they don’t offer robust protection to the unvaccinated. But once you reach a high enough level of vaccination, the disease gets effectively road-blocked. It can’t spread fast enough because it encounters too many vaccinated individuals, and so the majority of the population (even the unvaccinated people) are protected.

Find out more here.

This post is from 2017, so it wasn’t written about covid, but I’m reblogging it again so people can see visually what herd immunity means and how it works! Just as a note, covid’s r-value (the average number of people who get infected by one infected person) is lower than what this is modeling, which is why it’s possible that 70% vaccination (+ previous infection) could still give us herd immunity to covid. Also, this gif doesn’t take into account social distancing, which lowers the number of connections between dots. So don’t take this as an exact model of how covid spreads, but rather as a general illustration of the concept of herd immunity. Also, it shows how even when herd immunity isn’t quite achieved, high levels of vaccination in the population still mean that the disease spreads more slowly and infects fewer people!