Out of 217 people on board, 128 tested positive for COVID-19—but only 24 of those people showed symptoms prior to testing. The remaining 104 people—81% of those who tested positive—had not experienced any symptoms, the researchers report.
There were also 10 instances of people testing negative even when their cabin mate tested positive, which the authors say suggests there were some false-negative test results.
It’s difficult to extrapolate the results to larger populations, since the people on board the ship were living in close quarters while entirely isolated from outside life for about a month. Even still, the results are a stark reminder of how likely COVID-19 is to spread within communities, and how difficult it can be to tell when it does.
That’s a particularly important lesson to consider as states reopen and nice weather eats away at many people’s resolve to stay home. The virus can and does spread undetected—and an asymptomatic case can still cause serious illness if it spreads to someone else. Until a vaccine is available, the safest way to keep coronavirus from spreading is to keep your distance from others, whether you’re sick or not.