These newest waves of cases in South Korea and elsewhere indicate that we’re heading into a dangerous new phase of the outbreak. The virus (formally known as SARS-CoV-2) is now routinely showing up in people who didn’t catch it from recently traveling to China. In places like Iran, we’re also seeing cases where the chain of transmission is a mystery. That means there are almost certainly blind spots where the virus is spreading in communities without detection. The more unwatched sparks of disease there are in a country, the more likely they’ll erupt into a full-blown wildfire that will sustain the outbreak and turn it into a pandemic…

“I believe the window of opportunity [to contain the outbreak] is still there, but that the window of opportunity is narrowing,” WHO Director General Tedros Adhanom Ghebreyesus said during a press conference held Friday.

On Friday, epidemiologists from the Imperial College London in the UK also released their latest report on the outbreak. They concluded the strict travel restrictions and quarantines implemented in China, which haven’t come without controversy, likely did slow down the outbreak globally. But the situation still looks dire. They estimated that two-thirds of all travel-related cases exported outside the country have gone unnoticed, “potentially resulting in multiple chains of as yet undetected human-to-human transmission outside mainland China.”