After months of data collection, scientists agree: The delta variant is the most contagious version of the coronavirus worldwide. It spreads about 225% faster than the original version of the virus, and it's currently dominating the outbreak in the United States.

A new study, published online Wednesday, sheds light on why. It finds that the variant grows more rapidly inside people's respiratory tracts and to much higher levels, researchers at the Guangdong Provincial Center for Disease Control and Prevention reported.

Read more at NPR...