Based on these studies, it seems about 20–80% of people infected with Covid-19 could show symptoms. If this range turns out to be correct – and we combine it with our estimate that one in 15 people with symptoms are being reported – it would mean that hundreds of thousands of people in the UK have probably been infected with Covid-19 already, but not tens of millions. Of course, all these early studies have limitations in how the data was collected and what groups were being studied. To understand how much infection there has actually been, what we need are studies that collect blood samples from the wider population and test for previous exposure to Covid-19. As it happens, this was the key point made by the Oxford researchers in their paper, and it’s one I fully agree with.
There is growing evidence that, on average, people who show Covid-19 symptoms have a 1–1.5% risk of death. This has been estimated in studies of data from Wuhan, early international cases, and the Diamond Princess (with data adjusted to account for the older age of the cruise ship passengers). But this 1–1.5% risk just tells us what happens to people who have clear symptoms. If, as the above studies suggest, only 20–80% of infections come with symptoms, it would mean that for every 100,000 people who get infected with Covid-19, we would expect somewhere in the region of 200–1,200 deaths (ie between 100,000 x 20% x 1% and 100,000 x 80% x 1.5%).