How many Covid diagnoses are false positives?

Test, test, test said the WHO. And globally, that’s what everyone did: tests have detected more than 14 million cases of Sars-CoV-2 so far. The thinking goes: turn up, have your test, and if positive, you must have the disease. But that’s far from the truth. When virus levels in the population are very low, the chances of a test accurately detecting Covid-19 could be even less than 50 per cent – for reasons that are not widely understood. There are two issues about tests to get your head around. The first is the sensitivity of the test: the proportion of people who test positive, out of the population who