People walk along Ocean Drive on March 21, 2021 in Miami Beach, Florida. College students have arrived in the South Florida area for the annual spring break ritual and have urged city officials to impose a curfew from 8 p.m. to 6 a.m. while the coronavirus pandemic continues.

Joe Raedle | Getty Images

More and more younger adults in their thirties and forties are being admitted to hospitals with severe cases of Covid-19, said Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention on Wednesday.

“Data suggests this is all happening as we see an increasing spread of variants. 52 jurisdictions are now reporting cases of worrying variants,” Walensky said at a press conference on the pandemic.

Scientists say new variants of the coronavirus are more transmissible and some of them can also be more deadly, leading to more severe cases.

The highly contagious B.1.1.7 variant from the United Kingdom has become the dominant strain circulating in the United States, according to Walensky.

Walensky previously warned that spring break trips could lead to a renewed spike in cases, particularly in Florida, where the variant was rapidly spreading.

“I implore you, for the sake of our nation’s health,” Walensky said at a briefing last month. “The cases rose last spring, they rose again in the summer, they will climb now if we stop taking precautions, if more and more people are being vaccinated.”

Variant B.1.1.7 has now spread and now includes more than 16,000 cases in 52 jurisdictions in the country. The variant is about 50% more transmissible than the original wild strain of the coronavirus.