Why isn’t Matt Hancock taking Covid false positives seriously?

As Matt Hancock was doing his media round this morning, it was refreshing to hear him finally being questioned about the challenge of false positives. But his response made me worry whether the Health Secretary really knows what a false positive is – or the potential extent of the problem when it comes to detecting coronavirus and the impact of that on decision making.

False positives happen when someone is incorrectly given a positive result for something which in fact they do not have. As I wrote in May, no matter how carefully designed, created or performed, no test is perfect. Each test is given a sensitivity rating (the ability of the test to detect people who have a virus) and specificity rating (the ability of the test to correctly identify that a person does not have a virus).

The manufacturers of the UK’s RT-PCR tests report that the specificity of those tests is around 99 per cent, meaning that up to one per cent of cases are false positives.