One of the most troubling coronavirus trends to emerge in recent days is the deaths of so many young people who had no known underlying health conditions.
In Britain alone, they include a 13-year-old boy from Brixton in south London, 19-year-old chef Luca Di Nicola, 21-year-old Chloe Middleton and NHS nurse Areema Nasreen, 36.
Their deaths have stunned their families, who said each one was thought to be healthy and had never been diagnosed with any pre-existing conditions that would have made them vulnerable to Covid-19.
While the new strain of coronavirus appears to most seriously affect the elderly, experts in the US have been trying to find out why some healthy and younger people are dying - and they believe they have found some