It took six months for the world to reach 10 million confirmed cases of the coronavirus. It took just over six weeks for that number to double. The worldwide count of known COVID-19 infections climbed past 20 million on Monday, more than half of them from the U.S., India and Brazil. That’s according to the tally kept by Johns Hopkins University. The real infection numbers are believed to be much higher, given limitations on testing and the many mild cases that have gone unreported.