As the lockdown in China lifts across its cities, the authorities are turning their attention to a potential second wave. As of this month, Beijing is starting to release its daily data on asymptomatic carriers of the coronavirus. The British Medical Journal crunched the data: the first day, it said, showed that of 166 new infections across the country, 130 of them were asymptomatic (78 per cent). Tom Jefferson, an Oxford epidemiologist, commented on the data to the British Medical Journal:
'The sample is small, and more data will become available. Also, it’s not clear exactly how these cases were identified. But let’s just say they are generalisable. And even if they are 10 per cent out, then this suggests the virus is everywhere. If—and I stress, if—the results are representative, then we have to ask, "What the hell are we locking down for?" '
The sample was small - just one day - but we now have six days' data. I've looked at figures. Follow the methodology from the BMJ study and it gives 624 new cases, of which 434 of those asymptomatic - giving a ratio of 70pc. Each day's data is released separately, which you can find here: 31 Mar, Apr 1, 2, 3, 4, and 5.
NB: The data is not a general population sample. China's National Health Commission makes clear that these studies are from three different populations: international arrivals, the quarantined close contacts and the general public.