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After months of data collection, scientists agree: The delta variant is the most contagious version of the coronavirus worldwide. It spreads about 

 than the original version of the virus, and it's currently dominating the outbreak in the United States.

 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 report. 

On average, people infected with the delta variant had about 1,000 times more copies of the virus in their respiratory tracts than people infected with the original strain of the coronavirus, the study reports. 

In addition, after someone catches the delta variant, the person likely becomes infectious sooner. On average, it took only about four days for the delta variant to reach detectable levels inside a person, compared with six days for the original coronavirus variant. 

In the study, scientists analyzed COVID-19 patients involved in the first outbreak of the delta variant in mainland China, which occurred between May 21 and June 18 in Guangzhou, the capital city of Guangdong province. The researchers measured the levels of virus in 62 people involved in that outbreak and compared them with the levels in 63 patients infected back in 2020 with an early version of the virus. 

Their findings suggest that people who have contracted the delta variant are likely spreading the virus earlier in the course of their infection. 

And the scientists underscore the importance of quarantining immediately for 14 days after coming into contact with someone diagnosed with COVID-19, as the U.S. Centers for Disease Control and Prevention recommends. 

Or even better, getting fully vaccinated. Preliminary data shows that in some U.S. states, 99.5 percent of COVID-19 deaths in the past few months were among people who weren't vaccinated, the CDC's director, Dr. Rochelle Walensky, said Thursday at the White House.

"We know that the delta variant ... is currently surging in pockets of the country with low vaccination rates," she said. "We also know that our authorized vaccines prevent severe disease, hospitalization and death from the delta variant." 

Health

COVID-19

Michaeleen Doucleff

Author

New research from China suggests people infected with the delta variant have, on average, about 1,000 times more virus in their respiratory tracts than people infected with the original strain.

The delta variant isn't just hyper-contagious. It also grows more rapidly inside you

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