Have you heard of herd immunity (HI)?
It is a concept in certain infectious diseases, specifically ones that are contagious. The technical definition of HI is what occurs when a large proportion of a community (herd) becomes immune to a disease, making the spread of the disease from person to person unlikely. As a result the entire community is protected. What percentage of the herd needs to be infected to achieve it for Covid-19 is the mystery. It varies for other infections as well.
There are two methods of achieving HI. One is via natural infection, letting it run amok through the herd, which often sacrifices many lives, as in measles. The other is through vaccination without causing illness and death. While not perfect, it is a far better option.
HI, also called herd effect, or community or population or social immunity, was noted scientifically in 1923 in mouse experiments, examining disease death rates among groups with varying degrees of immunity. HI was first recognized as such in the 1930s through observing the measles infection patterns in children in Boston. It was noted the number of new infections temporarily decreased, particularly among susceptible youngsters after many kiddos were infected and became immune.
The original HI was purposefully induced with the smallpox vaccine in the late 1800s. Edward Jenner observed that milkmaids exposed to cowpox seemed unable to contract smallpox. He created the first smallpox vaccine from cowpox material. The Latin word for cow is vacca.
Vaccination remains the primary mode of creating HI. It is much safer than letting a natural infection like COVID-19 run rampant through the “herd” to produce unneeded deaths and great economic and social devastation. The word immune has an interesting derivation, coming from the Latin immunis, which means free from public service. Munus, Latin, is a duty, tax, or burden. By extension it has come to mean exempt from or protected against things that are a burden or harmful.
In a population or herd where a large number of individuals are immune, chains of infection are likely to be disrupted or stopped. Measles prevention via vaccine has been a primary example, along with so many other evil, disabling, or deadly infections like diphtheria, tetanus, whooping cough, mumps, etc. The theory derived from these observations holds that a certain threshold of immunity in the herd must be achieved to reach group immunity. What percent necessary may vary 60 to 90% by disease.
Another example of HI from vaccination is chickenpox. That vaccine was introduced in U.S. in 1995. In the following years the death rate from chickenpox (yes, chickenpox can kill) dropped by as much as 97%. Even though the vaccination cannot be given to infants, their death rate between 2004 and 2007 was zero, nada, none, zip, thanks to HI.
HI can eventually eliminate an infection such as smallpox from a large group. When this can be attained worldwide, it is labeled eradication, which is what happened to smallpox in 1977. It is possible for other diseases, but there has not been the vaccination cooperation on a global scale to accomplish it for any other microbe. When people choose not to become vaccinated for any number of beliefs, they are called “free riders.” They rely on the herd’s total immunity for their protection, which fails if enough follow that line. Then HI is lost.
So-called natural immunity from prior infections can wane in a herd over time, and folks start getting sick from it again until a new level of HI is established. A classic example of that would be a mild viral illness called erythema infectiosum, aka fifth disease, or “slapped cheek” disease due to the rosy red cheeks of infected kids. For a few years kids pop up with it until HI sets in. Then it seems to be gone for some years, and recurs when HI wanes, and kids start getting sick from it again.
Without venturing into the snake pit of the vicious political battle over HI vs. masks and “lockdowns,” the scientists who are the heads of our CDC and the WHO have rejected letting HI develop as a “fringe” approach. However, it is being pushed by administrative forces to avoid looking bad in an election year. A strange document has emerged from the mists called the Great Barrington Declaration, allegedly signed by thousands of people. The New York Times has found it has been signed by such fake names as Dr. Johnny Bananas, Dr. I.P. Freely, and Dr. Person Fake name. Credible science?
We hope for a vaccine that is effective and safe, which will not be soon. There is also the probability that a second, different mutation of the virus can cause reinfection in someone who has recovered from a first infection, as documented recently. We have needed a vaccine for years and centuries to prevent us from being infected by the poisonous proclamations of bloviating politicians. There’s a lot of infectious, injurious material to study. I hope this has sufficiently herded you through HI.
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