Shanghai’s 99.9% false positive rate shows China’s lockdowns are unnecessary and constitute human rights abuse
China’s mass Covid-19 testing programs are guaranteed to result in a vast majority of false positives and yet these are reported as “cases,” justifying lockdowns of 26% of China’s population and untold suffering
China has fully locked down its largest city, Shanghai, with a population of almost 26 million people. And the New York Times reports that about 373 million people, or 26% of China’s massive population, were under lockdown as of mid-April.
Shanghai’s incarcerated residents have started to protest, including in this Orwellian video of tower residents wailing their pain to each other.
Are these policies justified? Is there actually a dangerous pandemic in Shanghai that could explain these horrifically draconian lockdown policies?
The US FDA warned way back in November 2020 about the potential for very high false positives with antigen tests and Covid-19 screening programs. They stated that even a test that is 98% accurate in the lab (specificity) may produce 96% false positives in the field when the prevalence of Covid-19 in the general population is low (0.1% in this example that FDA itself provides in its warning).
Since that warning was issued by the FDA we’ve seen this low prevalence situation unfold in the real world in a number of jurisdictions. We can do the math fairly easily, for example, with respect to expected false positives resulting from massive, population-wide, antigen test Covid-19 screening programs like those being conducted in Shanghai.
So let’s do the math.
Assuming an even 26 million people living in Shanghai and assuming just one test per person (it’s probably quite a bit more than that because of multiple tests for at least some people as city-wide screening programs ramped up), we have 26 million antigen tests conducted regardless of the presence of any Covid-19 symptoms.
A recent study published in the top-ranked US medical journal JAMA, Connor et al. 2022, “Comparative Effectiveness of Single vs Repeated Rapid SARS-CoV-2 Antigen Testing Among Asymptomatic Individuals in a Workplace Setting,” found a 62% false positive rate in workplace screening programs in the US using Covid-19 antigen tests. Applying standard epidemiology regarding “positive predictive value,” this gives us a 98.9% specificity (chance of a negative test result being a true negative) for the antigen tests, at an assumed 1% Covid-19 “background prevalence.”
In order to calculate the number of likely false positives in Shanghai’s mass testing program we need to know the local background prevalence of Covid-19, or at least a reasonable starting estimate. We can in fact use the recent Shanghai city-wide Covid-19 screening program figures as a starting estimate for background prevalence to plug into our calculator.
Johns Hopkins University reported a seven-day average of 1,413 confirmed cases in Shanghai as of April 15. (Western media have also reported Shanghai’s unconfirmed cases, which on April 11 totaled about 26,000, the vast majority of which were asymptomatic; in China’s reporting these are considered suspected cases rather than confirmed cases.)
The seven-day daily average of 1,413 confirmed cases, assuming an active infection lasts about seven days, yields a background prevalence for Covid-19 in Shanghai of 1,413 times 7 divided by 26 million = ~0.04%.
Plugging these various figures into the British Medical Journal’s handy antigen test accuracy calculator, which gives the likelihood of a test positive or negative being accurate, we see that there is less than a 0.01% chance that a positive test result from Shanghai’s city-wide screening program is a true positive. This figure is known as the “positive predictive value.” The complement of this figure, which is 99.99%, is the “false positive rate.”
So, yes, based on these publicly available statistics and well-established epidemiological math, we see 99.99% of Shanghai’s test positives are very likely just false positives. This means that of approximately 26,000 new “asymptomatic cases” in Shanghai on April 11, described above, perhaps just 2 or 3 of these are true positives.
In other words, almost ALL of Shanghai’s positive test results are false positives.
We could plug this new background prevalence figure back into the calculator (this is how Bayesian iterative logic works) and find an even higher false positive rate but I think I’ve demonstrated my point already well enough.
For those confirmed cases that are PCR-verified after an antigen test positive, the chance of a false positive on both tests is quite a bit lower.
The bottomline is that Shanghai is locking down, literally locking people inside their homes, 26 million people based on what is nothing more than a tiny number of true positives.
This is authoritarian incompetence and cruelty at its absolute worst.
BMJ published our “rapid response” essay to their calculator and the massive false positives issue in June of 2021, and we explain in that essay how the math and policy choices are conspiring to create an illusion of a serious pandemic when in most jurisdictions around the world the same issues have been present that I’ve demonstrated for Shanghai — a vast exaggeration of all public statistics from “cases” to “hospitalizations” to “Covid deaths.”
This pandemic won’t end until public health officials and elected officials get their heads around just how inaccurate our testing systems are and how they are massively distorting the appearance of harm.