The speed of the spread of the Delta variant has seen a surge in COVID-19 cases as parts of the world, such as the UK and U.S., relax restrictions. But is it because the variant is more dangerous than previous variants?

U.S. virologist Vincent Racaniello and his colleagues wrote a piece in The New York Times suggesting human behavior is far more important in shaping the course of the pandemic than any variant. 

Emma Keeling interviewed him to find out more.