What is Herd Immunity?

True or false: In order to prevent the spread of the flu (or any other contagious disease) everyone needs to be vaccinated. False.

The reason this is false is that vaccination does not rely on 100% compliance. If it did, it would be completely ineffective in the real world. Instead, vaccination relies on something called herd immunity.

To understand herd immunity, imagine a community (or “herd”) that is composed entirely of people who have no immunity to a certain contagious disease (let’s call it Disease X).

Now imagine that just one person who is exposed to Disease X (known as “Patient Zero” in epidemiological circles), enters the community. Patient Zero will transmit it to everyone they come in contact with, who will transmit to everyone they come in contact with.

It is easy to see that in a short amount of time, everyone in the community will be exposed to Disease X.

But what happens if half of the community is immunized against Disease X? Well, Patient Zero will only infect half the people they come in contact with. Will Disease X still spread through the community? Yes, but much more slowly, and it will infect much fewer people.

And — importantly — it is not only the people who are vaccinated who are protected.

Let’s try one more thought experiment:

Imagine that Patient Zero only comes in contact with one person (let’s call them Person One), and Person One is the only person who comes in contact with one other person, whom we will call Person Two. Unfortunately, Person Two cannot be vaccinated for some reason. Perhaps they are allergic to the vaccine, or have some other contraindication.

Person One will not come down with Disease X, despite continued contact with Patient Zero. But not only is Person One immune, Person Two is immune as well.

Why? Because they only come in contact with Person One, and Person One cannot transmit the disease. And why is that? Because Person One was vaccinated.

Of course, most of us don’t live in three-person communities, but it should be clear how this concept scales to real-world communities. The people who are vaccinated provide a sort of shield against infection for their unvaccinated contacts.

This means that fewer than 100% of a community needs to be immunized against a disease to provide near-complete protection for the entire community. (How much fewer? That depends on how contagious the specific disease is.)

Still confused? Well, if a picture is worth a thousand words, a video must be worth at least ten thousand. Watch the simulation below to see how a disease spreads through a population, depending on what percentage of that population is vaccinated.

And if you think that you don’t need to get vaccinated against the flu, and can just rely on herd immunity, let’s do one last thought experiment:

Imagine if everyone thought that. Yup, no one would be immune, and our communities would be ravaged by the flu.

So don’t just be one of the herd. Get vaccinated.

At Laurel Bay Health and Rehabilitation Center, in the scenic beach town of Keansburg, NJ, we leave no aspect of our residents’ health to chance. We provide a tailored program of physical, occupational and speech therapy, as well as all types of specialized care under one roof. Our goal: getting our patients back to their optimal level of functioning and independence as quickly as possible, and that includes keeping them safe from infectious disease.

Read our reviews on senioradvisor.com, wellness.comand caring.com to hear what our residents and their families have to say.

Or better yet, come see for yourself contact us to schedule a tour by calling (372) 787-8100, or by clicking here.

Herd Immunity: Why your vaccinations help others


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