What makes Covid-19 so deadly is that so many infected people get no symptoms.
Without knowing they have it, the infected can then pass the disease to the more vulnerable, who risk dying.
In Britain, one of the world’s top Covid-19 hotspots, new data shows that 70% who tested positive showed no symptoms a week before and after the test. Almost 40,000 people in Britain have died of the disease.
The data shows it’s more important than ever to test as widely as possible.