Please Read This Re Covid19 Testing

City Journal is running an excellent article on Covid19 testing. It's especially important to understand the problems involved in the type of testing that was recently conducted in California. Most of the testing done in the US currently is done on persons who are exhibiting relatively serious symptoms that at least raise a concern that the SARS-CoV-2 virus is involved. The two sets of tests from California, on the other hand, attempted to establish the degree to which the virus may have spread in the general population--including those who are exhibiting no symptoms. The problems with this type of testing begin with the fact that the tests used were not FDA approved and had a very low level of specificity (more on that below). These tests, it turns out, had a specificity of only 90-95%--read on and you'll see why that makes those test results highly problematic--and very controversial among scientists.

In addition to the difficulties of interpreting test results of this type from a statistical standpoint, there are also problems caused by the fact that SARS-CoV-2 is not the only coronavirus circulating in the US. That can give rise to false positives, with no way of readily distinguishing the false positives from the real thing.

Beyond those problems, the testing tells us very little about the central concern with regard to this virus: immunity. Unfortunately many people labor under the misconception that Immunity is a simple binary phenomenon--if you test positive for coronavirus antibodies you have immunity, if you don't you don't. That is not the case. Immunity comes in degrees, and the presence of antibodies in and of itself does not guarantee an effective immunity has been developed. Unfortunately, our tests don't do a good job of assessing that. Furthermore, testing can't tell us how long immunity will last.

All these things have to be taken into account in assessing proper policy responses to the pandemic. Add to that the uncertainty caused by what I consider the high probability that SARS-CoV-2 is a virus that has been enhanced with "gain of function" features through molecular engineering. Here are some fairly extensive excerpts:

Understanding How Testing Works 

Challenges remain in accurately detecting Covid-19 infection. 

Peter Kolchinsky 

April 22, 2020

Expanded and frequent Covid-19 testing has emerged as a necessary precondition for reopening America and resuming something like normal life. But political leaders and citizens need a better understanding of how testing works, how testing can go wrong, and why tests don’t necessarily indicate immunity to disease. ...

...

... antibodies do not recognize the whole virus; each antibody—essentially trained to recognize a piece of a puzzle but not the whole—binds only to a small piece of the virus. The antibodies made by a person previously infected with SARS-CoV-2 may not recognize the parts of the virus used in a particular diagnostic lab test. Or maybe the person’s immune system only needed to develop a small amount of antibodies, beneath the level that a test could detect. In either case, the test would show that the person didn’t have antibodies to SARS-CoV-2, delivering a “false-negative” result.

If a test is 97 percent sensitive for prior SARS-CoV-2 infection, it means that out of 100 people recovered from the virus, it will incorrectly tell three that they don’t have antibodies—leading them to believe, erroneously, that they were never infected. ...

But it’s also possible that a serology test might indicate antibodies to SARS-CoV-2 when the subject was never exposed to it. We’ve all been infected with several, if not all, of the four human coronaviruses that circulate each year causing common colds, and so we already have some antibodies against those viruses. Sometimes these antibodies can bind to part of SARS-CoV-2, not well enough to protect a person from infection but well enough to turn a serology test positive. SARS-CoV-2 is generally unrecognizable to our immune systems, which is why it is causing this pandemic. If it were more similar to existing coronaviruses, it would probably have caused milder to no infection in most people. And yet, what little similarity it has to common cold viruses can trick serology tests into telling people they have recovered from SARS-CoV-2, when in fact they remain vulnerable. That’s a potentially deadly trick.

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In testing, epidemiologists distinguish between specificity—the ability of a test to tell a person who is truly negative that they are negative—and sensitivity, which is the ability of a test to tell a person who is truly positive that they are positive. ...

Studies that tested thousands of people in various regions have concluded that 2 percent or 3 percent of a given population have been infected, more than was previously thought. In these cases, it’s important to look at the specificity of the test that was used. If a test has a specificity between 98 percent and 99.9 percent, it could report as few as 0.1 percent of people false positive, or as many as 2 percent of everyone false positive. Thus, a study that reports that 3 percent of people have been infected might overestimate that share enormously if 2 percent—two-thirds of the presumed infected—are in fact false positives.

This has big implications for our estimates of lethality. If you think there are 100 deaths out of 30,000 infected people, that’s a lethality of 0.33 percent, but if it turns out that 20,000 of those people were actually false positives, then those 100 deaths were out of 10,000 people, which raises the rate of lethality to 1 percent. ...

The meaning of getting a positive result also depends on the infection rate. If 50 percent of people have been infected, then a test with a 97 percent sensitivity and a 2 percent false-positive rate is still likely to be 98 percent right if it tells you you’re positive. If only 2 percent of people are infected, then such a test would be only 50 percent right if it said you’re positive. A test result should be read as a probability, not a certainty. ...

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Another word of caution: while recovering from Covid-19 will most likely allow your immune system to generate antibodies and make you immune to reinfection—at least for a time—not everyone will necessarily become immune. It’s possible that some people will recover from a very mild infection with just enough antibodies to register “positive” on a serological test, but not enough to prevent a reinfection. ... until we have completed studies to quantify how many antibodies people have, and how those levels correlate with protection against reinfection, we can’t be sure that everyone who is simply positive for some antibodies is immune.

Moderate immunity might not prevent infection but could keep the virus from spreading to the lungs, resulting in a mild or even asymptomatic infection. However, that might still allow the virus to infect and replicate in a person’s nose and throat, which could spread the virus to others. ...

This would mean continuing to practice social distancing whenever possible and wearing a mask when around vulnerable people, just in case you might be asymptomatically carrying the virus. ...