Herd immunity


It’s time for a slight confession, I have been at a university of some sort as a student for close to 10 years. During this long time I have seen a number of things! Great things! But what I’d like to write about now is vaccinations. Another confession, I have not been vaccinated for Mumps, Measles or Rubella, which the vaccination is known as MMR. I wasn’t living in the UK when these vaccination normally are performed and I believe I was also thought to be allergic to egg proteins which made up part of the vaccine or something else in the vaccine long story short I just never got one. During my long stay at university’s, 3 in total, I have seen 4 out breaks of Mumps and not once caught it! I have managed to catch freshers flu 6 times in total so we know my immune system has it’s blind spots. So have I just been lucky in not catching mumps during this time? Well yes! But... there is another deeper reason behind my lucky escapes.

You may or not have heard of herd immunity, it’s often said that vaccinations are important to maintain herd immunity. But what is herd immunity? How can someone else vaccination stop me from becoming infected? Well I’ll get to that but this being a piece written about vaccinations I would be remiss not to mention antivax propaganda. It’s utter bollocks! In an ideal world that would be a sufficient comment but antivax groups are well financed and supported by a number of celebrities. I’ll leave it to you to decided about reading further on this topic and move on.

 the two people responsible for ruining jim Carrey for me


Vaccinations work in a number of ways but underpinning each is the idea that your immune system can remember what it has seen and dealt with before. This is the reason why you tend to only get the chicken pox once a life time and are then immune to it. Your body’s immune system is capable of recognising the invader should it try get in again. Drugs, stress and some cancers have been known to stop this system from working so life long drug abusers can catch so called ‘childhood’ diseases more than once. Vaccines use parts of viruses or bacteria that are stable, meaning they don’t change structure often, and trick your immune system into thinking that it is been invaded and responding to the invasion which then leaves the memory of the infection so your immune system can respond much quicker and deadlier should the contagion come around again.


pressure cooking kids was all the range before nintendo

Back to the topic on hand now you have a primer. Herd immunity allows people who are not protected by vaccination to receive some benefit from the herd. This works due to another tie in. You know people, it’s an educated guess that you probably have a close group of 10-20 friends and in total you know reasonably well, 150 or so people. By ‘know’ I mean you are capable of recalling their first name not necessarily people you would go to the pub or bowling with. This is known as a Dunbar’s number. It is thought that this number is the largest most people can maintain a social group and keep track of all the complex social interactions that go on with in a group this size.

You interact with these people as well as people you don’t know but for the sake of ease lets just say its people you know. Now I want you to imagine that you and all the people you know are little nodes or island and each is connected with lines to lets say 6 random places. Well done you, you’ve just created a network! Each of these lines is a possible way in which a disease can spread around. Now here’s were a little bit of magical maths comes in to effect depending on the reproductive rates of the disease there is a certain level of vaccination required in order to protect unvaccinated people on average.

If of 150 people you know all but two are fully vaccinated some random person and yourself the chances of the disease spreading to you are low unless you come into direct contact with that person which in our random example only happens 4% of the time. If you do not have contact the disease has no way of infecting you without going through vaccinated people which it can’t do! (most of the time). This means that the lower the level of unvaccinated people the more routes a disease has of getting around a population. The normal vaccination rates aimed for certain diseases is around 80% but it depends on the diseases and how it spreads. Once you reach vaccination rates below 80% odd things start happening where the number of routes open to the pathogen is large enough to get to the 20% or more people who are not vaccinated.

So herd immunity is exactly that, it is the immunity conferred from a diseases spreading to unvaccinated individuals by having its route of access blocked by the vaccinated members of a community. It is not a tangible thing that will stop you from getting the disease but it is a mathematical construct that limits the probability of people at risk from being infected. So to all the people out there who have been vaccinated, and to your parent, your actions have likely saved me from been infected any number of times by vicious and deadly pathogens for that, all I can say is thank you! Sincerely.

James Gurney

About Myles Power (555 Articles)
My name is Myles Power, and I run the educational YouTube channel, powerm1985. I spend what little free time I have sharing my love of SCIENCE! through home experiments, visiting sites of scientific interest, and angrily ranting at pseudoscience proponents. I am also one of the founding members of the podcast 'The League of Nerds' - which I co-host with James from 'The History of Infection'.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s