We’ve heard this term bandied about. Herd immunity. If we can acquire herd immunity, then COVID-19 will no longer be the scourge of our existence. When will that happen?
Basically, herd immunity means that there is a significant portion of a population that has acquired immunity (typically manifested as the presence of antibodies) to a contagious disease, so that further massive disease outbreaks are unlikely. A population manifests herd immunity when a significant portion have recovered from an outbreak of the disease or via inoculating enough people that an epidemic or pandemic is unlikely.
It doesn’t mean that there is no likelihood of developing the disease- it just means that the number of people who get infected is fewer and fewer each day. (You know- flattening the curve.)
This is why smallpox is considered to be eradicated. Enough folks either succumbed or were inoculated that by 1977 that smallpox was no longer a threat to the world’s population.
The critical value, the herd immunity threshold, involves assumptions, guesswork, and great data development. Because the computation involves the effective reproduction number (Re), which is related to the basic reproduction number (R0) that is derived from homogeneous populations.
Like we have homogeneous populations. Or, that everyone will be in contact with everyone else in a population. That barely applies if we live in small towns. Nowadays, we cluster- we are in routine contact with a set number of individuals and rarely interact with a bunch of others.
But, there’s more to herd immunity. We need to know S – the portion of the population who are susceptible to the infection. (S is also know as [1-p], where p is the proportion of the population that is immune to the disease. (Obviously, this means that p + S =1. And, that R0 X S =1.)
With enough algebraic manipulation, we can discern the equation that is more commonly seen:
p = 1 – (1/R0)
The lower the R0 , the lower the threshold to achieve immunity. The higher the R0, the higher the threshold that must be achieved for a population to develop herd immunity.
And, you guessed it- the best we an do is guess at the R0 for SARS-CoV-2. So, we have no idea if 60%, 70%, or 80% of the population will have to be inoculated (or have recovered from COVID-19) before we can relax all our social distancing and mask wearing.
The concept of when we achieve herd immunity is even more muddled. Dr. Fiona Harris (lead author) with 40 other professionals just published some cautionary results in JAMA. The article, Seroprevalence of Antibodies to SARS-CoV-2 in 10 Sites in the United States, is based on the fact that the presence of antibodies in one’s blood indicates prior infection; whether it involved asymptomatic, mild, or severe infections.
The results indicated that, dependent upon time and place, antibodies prevailed in between 1% and 6.9% of the population. And, in each population, the number of infections exceeded the number of reported cases.
https://app.flourish.studio/visualisation/2562261/4
The above link will make it clear how COVID-19 has changed our world.
But, it all boils down to the fact that we really have no idea where we are in this COVID-19 pandemic.
True we have no idea about the when what and how.COVID19 is changing the world and I want China to be held accountable.
I am not a fan of China- but they are not the problem. The person- and administration- to be held accountable is the USA’s President, who refused to acknowledge the facts, passed the blame to others, and would not provide a national response to protect the citizenry.
We don’t know, do we? The facts seem to change daily. Meanwhile, the county I live in has a record number of hospitalizations. The number is small compared to the outbreak states, but….it’s going up and up.
Alana recently posted..Garden Updates July 30 2020
Obviously, folks in your region have decided to put aside reason and caution. Be safe!
That chart in the link is SCARY!!! Your last line, we have no idea where we are in the Covid-19 pandemic…I doubt if we will know anytime in the near future.
Yeah. I tried to incorporate that chart- but failed. Glad you saw it.
Thanks for the visit, Martha.
This is the first time I have heard the word herd immunity. Just based on the word itself shows the mass media’s idea of what most humans are like them. The world has faced many mass diseases in the past and come though. We will with this as well. There are lessons to learn from all of this that the world needs to learn. We must unite as humans and stop separating ourselves by color, religion, race, and creed. Working together we can put an end to it.
Brenda Fluharty recently posted..Flash Fiction: Rain From Another Realm
Working together doing the right things- you are correct, Brenda! Thanks for the visit and the comment.