It’s a startling discovery that could help explain why the novel coronavirus has been so successful in spreading around the world. Nearly half of the Diamond Princess cruise-ship passengers and crew who tested positive for COVID-19 were asymptomatic when they were tested. The finding comes from a new report from the U.S. Centers for Disease Control and Prevention that has been seen by CNN. The report found that, of the 712 passengers and crew members who tested positive, 331 had absolutely no symptoms. Over the past few weeks, multiple studies have shown that people without symptoms can cause substantial amounts of infection. Another scary finding from the CDC report states that traces of the virus were found in cabins of infected passengers up to 17 days after the cabins were vacated, before deep cleaning had been carried out.