President Trump has called the coronavirus “the invisible enemy.” But when it comes to sanctions on North Korea, the pathogen may turn out to be his administration’s most effective ally.

North Korea’s fear of coronavirus infection appears to have achieved what Mr. Trump’s “maximum pressure” campaign against North Korean nuclear and missile work has not: choking the North’s economy by stopping its trafficking of coal and other goods, prohibited under United Nations sanctions, which is believed to be mostly with China.

According to a satellite-image analysis published Thursday by the Royal United Services Institute, a London-based research organization, and a review of additional satellite imagery by The New York Times, many North Korean commercial vessels that once carried sanctioned material to and from China — or transferred them illicitly ship-to-ship at sea — are now idled in their home ports.