n one cruise-ship coronavirus outbreak, more than 80% of people who tested positive for COVID-19 did not show any symptoms of the disease, according to a new paper published in the journal Thorax.
The research shows just how prevalent asymptomatic transmission of COVID-19 may be—a reality that both suggests official case counts are drastic underestimates, and emphasizes the importance of practicing social distancing even if you feel healthy.
Researchers have known for months that asymptomatic transmission of COVID-19 is possible and common, but without population-wide testing, it’s been difficult to estimate how many people get infected without showing symptoms. The new paper provides an example of how widespread asymptomatic transmission can be, at least in a contained environment.
The (unnamed) cruise ship in the new paper left Argentina in mid-March, with plans to travel around the Antarctic Peninsula and over to South Georgia Island in the south Atlantic ocean. All passengers were checked for coronavirus symptoms before departure, and people who had traveled through COVID-19 hotspots were not allowed on board.
Even still, a passenger developed a fever eight days into the trip, triggering a ship-wide lockdown. Crew members and additional passengers began to develop coronavirus symptoms over the next few days.
The ship was not allowed to re-dock in Argentina after the country closed its borders, so it continued on to Uruguay, where eight people were evacuated to a hospital. Uruguayan officials eventually arranged for everyone remaining on board to get tested before the boat docked.
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.