What is herd immunity & how do we get it?
Herd immunity is being talked about a lot recently, especially in relation to Covid 19 and the vaccination roll out.
According to the World Health Organisation in their 30/12 20 update,
'Herd immunity also known as population immunity is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity is developed through previous infection.
WHO supports achieving ‘herd immunity’ through vaccination, not by allowing disease to spread through any segment of the population, as this would result in unnecessary cases and deaths.'
So let’s have a deeper delve into what the concept of herd immunity is.
Firstly we all fall into 1 of three categories:
The fully susceptible population who have no prior immunity, may have high levels of exposure, have never been exposed to the infection before so you have no background immunity, you may have underlying health conditions, and are so described as vulnerable
Those who are partially immune or have some tolerance to infection due to previous exposure to some closely related viruses (currently coronaviruses such as the common cold), you may have some persistent immunity, low vulnerability ie. no underlying conditions, and you may have experienced some mild symptoms.
.You may be fully immune, resistant or tolerant to the viruses, (you have probably been exposed to SARS-CoV-2 previously) and you may also have a very strong innate immune system that functions well, no underlying vulnerabilities and if you are exposed you are either asymptomatic or are unaffected.
Of course we don’t all know which category we are in for certain, but what we do know is that during a pandemic the numbers of these 3 groups is going to change constantly.
Group 1, the fully susceptible will reduce the fastest as these people either unfortunately die, or develop partial immunity and move into group 2 or full immunity and move into group 3.
So who are the people in group 1?
Most likely you will be over 75, with underlying health conditions, you will have had a high viral load exposure, maybe due to hospital visits. You may be immune compromised, you probably have had no prior exposure to this particular virus or related viruses to give you any immunity, and you may have lost previous immunity over time. You may also have a susceptibility to antibody-derived enhancement (ADE) which means you have developed an antibody response either to a previous infection or to vaccination and then, when you are exposed to the disease you get seriously ill.
And what about group 2. The partially immune?
Well you will not be elderly, you’ll have no pre existing or underlying conditions, you have a healthy diet and lifestyle, you have good nutrients especially vitamin D, C and zinc. You will not be exposed to the virus on a high level, you have had some prior exposure to Covid 19 or closely related coronaviruses and you may have lost some of you immunity over time.
And finally, group 3, the fully immune?
You will also generally be younger, but many of the same factors apply as in group 2.
So what happens when you become immune?
Well, you could have a really strong innate immune response so that almost non of the virus enters your body and you are virtually asymptomatic.
Or you may have a slower, less competent immune system and the innate immune system doesn’t stop it entirely and it allows some of the virus in. Then your adaptive immune system comes into play over a period of days and prevents you developing a really serious disease.
There are a whole range of immune cells and compounds that are involved in the innate and adaptive immune system response that I will be touching on further in a piece. Including the microbiome and gut health to support the immune system.
Most research is focusing on just one of the types of the immune cells in our bodies and this alone is being studied for the vaccines.
However, we know that memory T cell immunity is also very important and that there are very few studies looking at this part of the immune system, for long term immunity. And this is what’s going to really back up naturally acquired immunity in the population.
Remember the numbers in the 3 groups are constantly changing, especially in the early stages as the new pathogen is at its most powerful in terms of impact in the early stages. The virus will create mutations along the way, or variants, which may be more transmissible but not necessarily more virulent.
Even without vaccination, the group 1 will become so small the epidemic can not grow any more and this is when we are reaching herd immunity. Moving forward the virus will be able to wax and wane or it may complete disappear as has happened historically with viruses.
So what about transmission rates?
Transmission rates or the R rate is something we are also told about and no doubt something we are all familiar with now. It is measured using a formula from the 1970s. If the R number is 1 or less, the disease will decline.
Sars-Cov-2 has an R rate of 2-3 in a completely susceptible population (the people in group 1) and this calculates to a need for 60-70 percent of the population needing to be immune to achieve herd immunity. This is where the vaccination target figures come from.
This assumes that all the population is in group1 and that mixing with other people will be random… neither of these are the case.
And, as I previously mentioned here, I want to remind you that T cell immunity is the most important for long term immunity as I understand it, and and we are not measuring it. With T cell immunity, herd immunity can actually be achieved at a much lower level of just 10-20 percent.
So, the big question is what role do vaccines play?
Vaccines try to achieve immunity without exposure to the actual disease. The new vaccines we have for Covid 19 are very different to any we have seen before.
MRNA vaccines (Moderna & Pfizer) programme your muscle cells to produce the spike protein so your body becomes the vaccine factory, whereas the Astra Zeneca and Oxford vaccines take a synthetic DNA sequence and place it inside a genetically modified chimpanzee virus and then injects it into your body so the body has an immune reaction.
The hope is of course that this does not create harm, but there is no such thing as a vaccine that creates no harm. We are at a very early stage of understanding the adverse drug reactions of these brand new vaccines and logic says it will take months even years for these to be fully understood. We also now understand that transmission is not stopped by these vaccines and more data will follow on this.
So why might this virus decline?
It will not decline solely as a result of vaccination, there are multiple factors to consider, we know historically, many infectious diseases have declined way before any vaccination was introduced, TB & smallpox to name just two.
We know that exposure and therefore herd immunity is rising in the population. This means the susceptible group 1 people are also declining in numbers.
We must consider other influences such as population mixing, crowding, ventilation, working together, the virulence of the virus, the transmission rate, the nutritional status of the person, any pre existing conditions, your immune competence, prior exposure as well as any effective vaccination.
Vaccination is not the only option, it is just a part of the picture and there are many things we can all do to improve our overall immune status.
First, look at your nutritional status and optimise it! Include Vitamin C, Vitamin D and Zinc in your regime.
Reduce your vulnerability to underlying conditions which tax your immune system and make you more susceptible to new ones coming along. That means improve your resilience.
Educate yourself, read around the subject of health and what you can do to help yourself and make a difference. I believe it is an inside job and we can do so much ourselves to raise our vital force.
Finally, engage with health practitioners, look at websites, and look at kick starting your health from where you are now.
Until next time, Polly x