Data collection for the study, conducted from May to November 2020, involved a population of almost 3,000 U.S. Marine Corps recruits taking part in the COVID-19 Health Action Response for Marines (CHARM) study.

A key finding in the study was a difference in the innate immune response to SARS-CoV-2 (the virus that causes COVID-19) between men and women. On average, women’s innate immune systems are able to produce greater amounts of interferon in the initial stages of infection than men’s. Interferon, a substance produced in the body by white blood cells, is part of a body’s innate immune system – the part of the immune system that begins fighting off infection and signaling to other cells that something is wrong before the body ever begins producing antibodies.

“This means that women tend to have a more robust immune response when they first encounter this new virus,” said Cmdr. Andrew Letizia, current science director at NMRC’s Naval Medical Research Unit-2, who led the NMRC team conducting the CHARM study in 2020. “Even among mild to moderate cases, women have a notably better immune reaction, and recover faster than men.”

Data from this study informed adjustments to Marine policy on quarantining in July 2020, lowering the required days of isolation for infected individuals, both male and female, from 14 to 10 days. This adjustment came a full three months before similar changes to the national U.S. policy, and benefitted both individual recruits and the Marines.

“Every day a recruit is in isolation, they aren’t training. That costs the Marines money, and impacts the quality of the recruit’s training,” Letizia explained. “When a Marine is in isolation for 14 days, they often get rolled into an entirely different platoon of Marines they don’t know, and it becomes hard to develop the bonds and teambuilding skills that need to happen during training. The new quarantine period allows Marines to return to their original teams and retain those bonds.”

Volunteers provided periodic samples over the course of several weeks, regardless of whether they contracted SARS-CoV-2. Those who tested positive were isolated and had more frequent samples taken. Researchers were therefore able to collect data on participants before, during, and following infection, which provided a fuller picture of the immune response to the virus.

According to Letizia, NMRC and the DoD were uniquely positioned to conduct the research necessary for this study. The population sampled, U.S. Marine recruits, represented one of the few such communities that existed during the early months of lockdown in 2020.

“A lot of settings where young, healthy people congregate had shut down by March 2020,” Letizia said. “High schools, colleges, sporting events and a lot of working environments weren’t open, meaning there wasn’t another group of young people all together outside of military training and recruiting, which was still ongoing as a matter of national security.”

Findings from this study, and continued data collection from the recruits who volunteered for the CHARM study, have opened the door for future research in areas that could inform DoD policy concerning COVID-19, to include other variants of the corona virus, the effects of long COVID and the treatment of similar infections.

“This study was about finding out how women had better immune reactions,” Letizia explained. “As we understand more about why women are better able to fight off COVID, we can create future therapies to improve outcomes for patients.”

NMRC and its commands are engaged in a broad spectrum of activity from basic science in the laboratory to field studies in austere and remote areas of the world to investigations in operational environments. In support of the Navy, Marine Corps, and joint U.S. warfighters, researchers study infectious diseases, biological warfare detection and defense, combat casualty care, environmental health concerns, aerospace and undersea medicine, medical modeling, simulation, operational mission support, epidemiology, and behavioral sciences.