Researchers believe the Delta variant is able to make copies of itself inside the human body at a faster rate than others. That means infected people carry a much larger viral load - more than one thousand times larger in some cases.
That kind of viral load can spread to another person within a few minutes - even at distances of six feet or more.
The risk of infection is significantly higher in unvaccinated people - who account for 97% of hospitalizations and 99.5% of deaths.