Covid-19: Almost half of infections come from people with no symptoms

New research has concluded that four out of 10 transmissions of Covid-19 occur from people in the very early stages of Covid -19, before they show any symptoms. Luca Ferretti from Oxford Big Data Institute explains the numbers and why a joined up approach involving masks and distancing - along with tracking, tracing and isolating - is so crucial to containing the pandemic.

Photo:Women walk in the street in Pune, India Credit: Getty Images