The number of confirmed cases of the coronavirus in the United States surpassed 1 million on Tuesday, more than doubling in less than three weeks, according to data compiled by Johns Hopkins University .

The U.S., home to about 4% of the global population, has reported about one-third of the world’s more than 3 million known coronavirus infections. The first known cases of the virus in China began appearing in December. It took nearly four months for the number of confirmed cases in the U.S. to hit 500,000 on April 10.