Herd Immunity

Last week I wrote an article on meningitis W for Cotswold Allure website (click here to see the full text). In it, I mentioned a concept known as herd immunity (sometimes more poetically termed ‘community immunity’) and understanding the concept is central to the whole vaccine debate.

Herd immunity occurs when a high percentage of a population is vaccinated. Accordingly, diseases struggle to spread as there are very few susceptible individuals to infect.

Herd immunity

 

If we use measles as an example, 19 out of 20 people need to be immunised to ensure herd immunity. Thankfully, as a whole, UK vaccination rates are high. However, they do vary between regions and can, at times, be affected by bad publicity (no matter how erroneous that publicity might be). When vaccination rates decrease, the likelihood of disease outbreaks increases. The recent heavily publicised spate of measles cases in Disneyland occurred because of exactly this phenomenon (click here for further details). Additionally, herd immunity does not protect at all against some vaccine-preventable diseases. Tetanus, a disease cause by the Clostridium tetani bacterium, is caught from soil and faeces rather than other infected individuals.

So when parents decide to not to vaccinate their child, what knock on effects does that have? Firstly, it exposes their child to numerous potentially fatal, yet preventable diseases. Some of these parents may paradoxically have been relying on herd immunity to protect their non-immunised child. This is misplaced logic. Whilst herd immunity works at a population level to minimise disease outbreaks, it offer low levels of individual protection (unlike vaccines).

Secondly, it reduces the herd immunity effect, an effect which is vital to several groups of people who can not be safely immunised. These include;

Newborn babies

Patients with immune system problems

Chemotherapy patients

This issue has very recently hit the worldwide press because of the heartbreaking case of Riley Hughes, a 32 day old baby who died of whooping cough in Perth, Western Australia. I urge everyone to read this article from The Telegraph (click here).

Light for Riley

“Our hearts break for those of you who’ve endured similarly and we believe no parent should ever have to suffer this pain again”

But it’s not just newborns that are at risk. Click here to read about a family of four boys who have an inherited genetic immune deficiency illness. They do not produce antibodies to fight infections normally and hence are potentially vulnerable to many micro-organisms. Herd immunity helps to protect them. As their mum points out;

Vaccinating your kids is just as, if not more, immediately helpful to my kids and other vulnerable kids in your school or community. If you are a parent who is vaccine-hesitant or who has chosen not to vaccinate, my plea to you is this; My kids are my heart and soul, just as yours are to you, and I need your help to keep them healthy and safe. I would do the same for you”

So can we demonstrate that herd immunity actually exists? Well yes. As mentioned in my Cotswold Allure article, when the meningitis C immunisation was introduced, the incidence of the disease fell by 90% in the age groups who received the vaccine. But the incidence also fell by 65% in non-immunised groups, demonstrating herd immunity.

Vaccinating your child protects them and numerous others. Can you think of a good reason not to now? Worth pondering isn’t it? We’ll look at these possible reasons in the next blog…………………