Cruise ship offers transmission clues
Scientists trying to understand exactly how the coronavirus is transmitted have conducted a deep analysis of what might be the best case study of viral spread: the Covid-19 outbreak on board the Diamond Princess cruise ship. For researchers, the vessel was essentially a giant experimentin-a-bottle, reports The New York Times.
On Jan. 20, an infected person boarded the ship; a month later, more than 700 of the 3,711 passengers and crew had tested positive, and many became dangerously ill. The scientists ran more than 20,000 computer simulations of how the virus might have spread, each with different assumptions for social interactions, how long passengers spent in their cabins, and other factors.
Each simulation also took into account the contributions of virus-laden aerosols—tiny droplets emitted when a person speaks, breathes, coughs, or sneezes, which can float in the air for minutes and be breathed in—and larger droplets, which fall quickly to the ground. Many clinicians have argued that these larger droplets—which are similarly emitted and can infect surfaces or people, if they land on someone’s nose or mouth—are the primary means of transmission. But the new study found that about 60 percent of infections on the Diamond Princess were caused by tiny aerosols. Good ventilation didn’t prevent the virus spreading, the researchers noted, which suggests that people should wear masks even in well-ventilated spaces. “Many people have argued that airborne transmission is happening, but no one had numbers for it,” says study leader Parham Azimi, from Harvard University. “In this paper, we provide the first real estimates.”