News - World: The total number of COVID-19 cases in the United States topped 29.34 million on Friday, with the national death toll reaching 532,384, according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University.

Nearly 4,000 infection cases of coronavirus variants have been reported in the United States as of Thursday, according to the latest data of the US Centers for Disease Control and Prevention (CDC).

The number of variants reported will likely increase as more specimens are sequenced and if the frequency of variants increases, according to the CDC.

Experts are concerned about some worrisome variants that are in places like California and New York.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said in an interview Friday that he is "not surprised" that the COVID-19 pandemic is still spreading in the United States and the new variants of coronavirus is the biggest challenge for the country.