In this May 18, 2021, file photo, kindergarten students wear masks and are separated by plexiglass during a math lesson at the Milton Elementary School, in Rye, N.Y. Credit: Mary Altaffer / AP

WASHINGTON — The so-called COVID-19 delta variant — which was first detected in India — now represents more than 20 percent of coronavirus infections in the U.S. in the last two weeks.

It’s double what it was when the Centers for Disease Control last reported on the variant’s prevalence.

Dr. Anthony Fauci, the nation’s top infectious disease expert, warned that the U.S. could be following the United Kingdom’s course, where the variant has become the dominant strain due to rapid spread among youth.

Indications are that the COVID-19 vaccines remain effective against the variant, Fauci said.

The variant is accounting for half of new infections in the regions that include Iowa, Kansas, Missouri, Nebraska, Colorado, Montana, North Dakota, South Dakota, Utah and Wyoming.