Now a new problem has emerged: the original PHE tests, according to a memo sent by its senior lab team, were less reliable than first thought, struggling under the strain of mass reproduction. The memo, dated April 11, advises all PHE centres (12 in total) to “migrate” to a commercial test by April 23 – that is by Thursday.

The memo flags up a number of concerns about the PHE test, despite the fact hundreds of thousands have now been carried out. The problems, says the PHE, were first detected in March and showed that its effectiveness at the beginning was not matched in the mass roll out. The memo, sent out under the heading: “Updating PHE COVID-19 Diagnostic Test Protocols” details a number of concerns with how the original test is being carried out.

It highlights problems over the consistency of the tests – what the memo calls “diversity of molecular platforms, reagents, kits and assay performance” in the different labs; “quality assurance difficulties” for “key reagents”; a shortage of swabs and transport problems that may lead to tests being tainted; and problems with enzymes “from external suppliers” that were not up to the standard used in the original testing. Put simply: it raises serious questions about whether NHS workers were sent back into hospitals after recording negative coronavirus tests – when in fact they may well have had it.  

The fact the PHE test is now being ditched in favour of the commercial kits is not a shock. The system is supposed to work that way, with PHE accepting that its home-grown kit is always intended as a stopgap until the commercial kits come on stream.

One expert likened PHE’s approach Covid-19 testing to sending out a recipe and ingredients – leaving a margin for error, depending on the chef – while the process used by commercial firms is more like a ready meal supplied by a supermarket that comes out the same every time. 

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