Marine study shows COVID-19 transmission despite public health measures, strict quarantine

Editor's Note

This study of 1,848 US Marine Corps recruits finds that despite social distancing, wearing masks, regular handwashing, and other public health measures including strict quarantine, recruits contracted COVID-19 and spread it to others, even though hardly any of them had symptoms.

Study participants were told to isolate themselves for 2 weeks at home, and then they were in a supervised military quarantine at a closed college campus, The Citadel in Charleston, South Carolina, for 2 more weeks. This included having a single roommate, wearing cloth masks, keeping at least 6 feet apart, regular handwashing, and doing most training outdoors. They also had daily fever and symptom checks and were under constant supervision of Marine Corps instructors.

Within 2 days after arrival on campus, 16 tested positive for COVID-19, 15 of whom were asymptomatic. An additional 35 participants tested positive on day 7 or day 14. All 35 had tested negative on arrival and became positive during the supervised quarantine.

The researchers from the Icahn School of Medicine at Mount Sinai in New York and the Naval Medical Research Center, Silver Spring, Maryland, identified six independent transmission clusters defined by distinct mutations, which indicated there were multiple independent COVID-19 introductions and outbreaks during the supervised quarantine.

All cases were identified as the result of scheduled testing rather than testing performed as a result of daily screening or symptoms.

The findings have important implications for the effectiveness of public health measures to suppress the transmission of COVID-19 among young adults, whether in military training, schools, or other aspects of the pandemic, the researchers say.