Confirmed COVID-19 cases are up in some states, according to CDC data. Here's what to know the week of Sept. 8.

How exactly did the delta variant evolve into the highly infectious strain that the world is now struggling to contain? Scientists have a few theories.

The Delta variant, which was first detected in India, has prompted recent calls from President Joe Biden and Anthony Fauci for more Americans to get vaccinated.

The Centers for Disease Control and Prevention listed the COVID-19 delta variant as one of its "variants of concern" (VOCs) on June 15. According to the CDC, VOCs can be more contagious, more ...

The delta variant now accounts for 93% of all sequenced cases in the U.S., according to the latest CDC data.

The so-called delta variant is estimated to account for about 58% of all COVID-19 cases in the United States, according to the Centers for Disease Control and Prevention.

Is the mu variant worse than delta? What to know about COVID-19 mutations Right now, there are only a handful of concerning COVID-19 variants: alpha, beta, gamma and delta.