When anyone plays a game of chance knowing the odds is oftentimes helpful. For instance in Texas Hold ‘Em, if there is only one card left (“the river”), we don’t know if that ‘8’ that we need to fill an inside straight will appear. However, if one knows that catching an inside straight has about an 11:1-12:1 chance of success, then perhaps it would not be wise to bet the farm that ‘8’ will appear “on the river” to fill that inside straight. Certainly it might happen. We don’t know, but the odds are against it. Likewise, catching a ‘heart’ “on the river” to complete a flush is not 11-12:1, but rather more like 5:1. Will that heart come? We don’t know, but we do know the probability of that happening. Therefore, betting on completing that flush is much more likely to be successful compared to betting on filling that inside straight. Without bringing in the Texas Hold ‘Em concept of “pot odds,” this is merely an example of basic probability.
No matter the situation the laws of probability do not change. It doesn’t matter if the subject is poker or herd immunity.
What is herd immunity?
The general idea behind herd immunity is that in a population where many people are immune, a disease can’t take hold and grow into an epidemic, thereby protecting people who aren’t immune. The population (perhaps unfortunately called a herd ) protects vulnerable individuals.
So how many people in a population need to be immune to have herd immunity?
This can actually be figured out mathematically.
Warning: What follows is not meant to be understood by us mere mortals.
The following is based on a chapter from the book Understanding numbers by the Plus Editors Rachel Thomasand Marianne Freiberger.
Skipping all of the intermediate steps, to achieve herd immunity we need to make sure that at least a proportion of
of the population is immune. For an
of 2.5, the higher end of the estimates for COVID-19, this means that we need to get at least a proportion of
of the population immune. This translates to at least 60%. In other words, 60% of the population needs to be immune to this virus in order to achieve herd immunity to this virus.
How do we do this? Well, ideally we would do it by vaccinating at least 60% of the population. In the absence of a vaccine, we can hope that this level of immunity will be achieved naturally, by people becoming sick and then becoming immune.
So far this appears to be relatively straight forward, however then we get the “we don’t know crowd” involved.
When the logical question of: “Should People Who Had the Virus Defer Vaccination?”. . . the common sense answer is “Yes.” Since at the present time and for the foreseeable future there will not be enough vaccine to vaccinate everybody, it makes common sense to say, “Those who have already have the virus are probably immune, and so should at least go to the rear of the line. If one asks the experts how long the immunity to Covid will continue to last after an infection, the various answers will involve a lot of “we don’t know.” For example, Deborah Fuller, a vaccinoligist at University of Washington, said, “we don’t know how durable natural immunity is.” Come on, Ms. Fuller, of course we don’t know how long the natural immunity lasts, as Covid has only been with us for about ten months. When someone, like Ms. Fuller says something like that, she should be asked, “Do we know how long the immunity to the vaccine will last?” . . . “Err, really, we don’t know as the vaccine has also been around for only a relatively short period of time.”
The following is from an article in Health:
“To be clear, most experts do think an initial infection from the coronavirus, called SARS-CoV-2, will grant people immunity to the virus for some amount of time. That is generally the case with acute infections from other viruses, including other coronaviruses.”
Ah, a common sense statement. Yes, we do not know how long immunity to a native Covid infection lasts, but if we use common sense, we can assume that it will last for some unknown amount of time. So far, so good. Then would it not make sense to defer the vaccination of those who have already have had a documented Covid infection till some later date (perhaps never, depending on what happens with the the immunity of these individuals in the future.) If these already infected individuals do not get the vaccine now, then others who have not had Covid, can be vaccinated instead. Doing this will make the achievement of herd immunity occur more quickly, and that will be for the benefit of everybody.