Mounting evidence suggests the delta variant is the most contagious strain in the world, spreading about 225 percent faster than the original version of the virus. A small study published online July 7 may help explain why, NPR reported.

The delta variant, first identified in India, grows faster in people’s respiratory tracts and to much higher levels, according to researchers at the Guangdong Provincial Center for Disease Control and Prevention in China.

They analyzed virus levels in 62 people infected during China’s first delta variant outbreak between May 21 and June 18. They compared their findings to virus levels in 63 patients infected in 2020 by an earlier version of the virus.

On average, viral load was about 1,000 times higher for people infected with delta, compared to those infected with the earlier strain, researchers found. It also took about four days on average for delta to reach detectable levels in study participants, compared to six days for the other strain. This finding suggests people with delta likely become infectious sooner and are spreading the virus earlier in the course of their infection, researchers said. 

To view the full study, click here.