A mobile Covid-19 vaccination center in front of Bolton City Hall in Bolton, where the number of cases of the Delta variant identified for the first time in India was relatively high.

Peter Byrne | PA pictures | Getty Images

The Delta variant first identified in India now accounts for an estimated 83% of all sequenced Covid-19 cases in the United States, the director of the Centers for Disease Control and Prevention said Tuesday.

“This is a dramatic 50% increase in the week of July 3rd,” said CDC Director Dr. Rochelle Walensky during a Senate hearing.

The increase in delta cases leads to more deaths. Covid deaths rose nearly 48% over the past week to an average of 239 per day, she said.

“Every death is tragic and even more heartbreaking when we know that the majority of these deaths could be prevented with a simple, safe, and available vaccine,” she said.

Walensky said nearly two-thirds of counties in the US had less than 40% of their residents vaccinated, “allowing the highly transmissible Delta variant to emerge and spread rapidly.”

The variant is even more contagious than the alpha variant, which was first identified in the UK and has been estimated by health authorities there to be between 43% and 90% more transmissible than the original Covid-19 strain. The delta, discovered in October, has spread to more than 100 countries, according to the World Health Organization.

“The reason it is so impressive is the fact that it has the ability to transmit from person to person in an extraordinarily efficient manner, far beyond any other variant we have seen before,” Dr. Anthony Fauci, who said the senior medical advisor to the White House during the hearing.

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