PCR antigen tests give an indication of the presence of the virus in your system. They are based on swabs and do have a problem with both false negatives and positives. One could for example sample on the wrong side of a mucous membrane. They are not reliable for determining whether you have HAD the virus though in the past.
The antibody tests sample directly from your blood plasma (serum plasma) and give a measure of your antibody load. This will tell you if you have had the virus or not. In short they capture a greater swathe of the population. By all accounts these seem to show that in most Western countries between 3% to 10% (maybe higher) of the population have had or have the virus. Seems to be far higher in NYC which is consistent with their death rates, Several of these tests have been carried out in various locales for research purposes by epidemiology experts. They have significantly lower false positive and negative rates than the PCR test. They are however more expensive.
WHO itself has acknowledged that between 2%-4% of the world population likely has antibodies for the disease. This translates to a number somewhere in the order of 200 million people worldwide.
At present close to 4 million cases worldwide have been reported which begs the question...Where is the rest?
Two possible alternatives come to mind 1) Under reporting 2) High Asymptomatic Numbers. Under reporting can only hide the shortfall for so long as the exaggerated death rate would highlight this (unless the lethality is even far blower than it is). Asymptomatic Numbers offer an explanation which is consistent with studies of people who developed the Antibodies (showing the detection of virus by the Immune system).
The consensus now is that those falling into the Asymptomatic category may make up 80-90% of all those infected. They don't EVER show symptoms but will shed the virus during the time when they are infected, It is the presence of said individuals that has greatly spread the virus.
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