Implementing best practice public health measures on their own among young adults may not be enough to prevent SARS-CoV-2 transmission, and additional actions, such as widespread and repeated testing, are recommended to reduce the risk of viral spread, according to research published today in the New England Journal of Medicine.

Researchers from Naval Medical Research Center (NMRC), in collaboration with scientists from the Icahn School of Medicine at Mount Sinai, conducted a study to understand the dynamics of viral transmission and host response to COVID-19 in young adults in order to inform public health measures in response to COVID-19 in a group setting.

The study, COVID-19 Health Action Response for Marines (CHARM), took place at Marine Corps Recruit Depot Parris Island, South Carolina, and included nearly 2,000 participants, composed mostly of 18- to 20-year-old healthy Marine recruits predominantly from the Eastern United States. Upon arrival for recruit training, they spent two weeks in a strict, supervised group quarantine that required wearing masks and emphasized hand washing and social distancing as they began their initial military instruction, primarily outdoors.

To determine asymptomatic and symptomatic SARS-CoV-2 prevalence and transmission among study participants during the quarantine period, researchers collected study questionnaires and specimens weekly and conducted both polymerase chain reaction (PCR) and serology tests. PCR tests are the gold standard for diagnosing COVID-19.

"The study hopes to improve medical readiness for the Marines and the DoD as well as inform force health protection measures,” said Cmdr. Andrew Letizia lead researcher for the study and deputy director of NMRCs infectious diseases directorate. “The investigators and I believe these findings will help the DoD, other public health entities, and society as a whole mitigate the spread of the pandemic not only among this particular population, but to those they might unknowingly infect as well."

The authors also found that nearly 6% of study participants arrived to recruit training with antibodies for SARS-CoV-2, indicating a previous exposure to the virus. Additionally, at the start of the supervised quarantine, 1% of participants tested positive, 95% of whom were asymptomatic. All reported self-quarantine at home for two weeks before reporting, denied any direct exposure to sick contacts and did not have any risk factors for exposure to COVID-19. Therefore, questions assessing current symptoms or risk factors would not have identified 95% of these individuals who were infected.

According to the authors, these results suggest the need to augment public health measures with widespread initial and repeated surveillance testing to prevent COVID-19 transmission in group settings.