Sources in the fledgling Covid-19 testing industry tell me that it is not surprising Public Health England’s (PHE) antigen test may not have been as reliable as would have been desired.
An antigen is a structure within a virus that triggers the immune system's response to fight off the infection.
One source said: “The use of the temporary assay [testing procedure] has been associated with issues relating to diversity of platforms used, swabs, transport, etc.
"All these issues can lead to variability of results and you need to perfect every step of the process.
"This is also why having a limited number of qualified labs around the country is better than relying on a cottage industry of small labs for this test, it creates too much variability of results”.
All of which begs the question (again) why the government did not move earlier to set up the much bigger labs (the super labs) that it is now creating.
Apparently there are significant numbers of false negative results even with the most reliable tests and therefore America’s CDC (Centers for Disease Control) recommends doing the test twice.
Experts worldwide have estimated up to 20-30% of false negatives should be expected, hence the need to do the test twice.
It has certainly been very striking when UK testing stats are released that numbers of tests have always been consistently greater than numbers of people tested.
So it looks as though there has been a good deal of testing with the same individuals showing symptoms more than once.
But for the avoidance of doubt, the “well validated commercial tests being used in the four new super labs [in Milton Keynes, Glasgow, Alderley Park and Cambridge] have a sensitivity greater than 98%”.
Which is apparently much better than in PHE labs with their temporary assays.
In a nutshell, PHE’s "home brew" is intrinsically less reliable than a proper validated commercial test.