Why was this kind of research not done at the start of the pandemic?
At the start of the pandemic, very little was known about COVID-19 and the virus that causes the disease. As the pandemic progressed, more data and understanding have now emerged to guide decision making.
This study started after a period in which enough clinical data has been collected for a more robust and reliable analysis. Although the UK may be past the initial peak of the pandemic, as we move to ease lockdown measures and restore health services and economic activity, our understanding of the virus means doctors and nurses and policy makers can be better guided by the evidence collected so far to keep people safe now and in the future