Researchers might be one step closer to developing a “stress vaccine” that could prevent PTSD syndromes and reduce stressful reactions. The “vaccine” was developed from a bacterium naturally found in soil. This bacterium, Mycobacterium vaccae (M. vaccae) has been shown to reduce inflammation associated with the body’s stress response. Who knew dirt could be so helpful?

The vaccine works off the idea of “old friends,” a scientific theory that humans developed alongside organisms that used to help prevent things like allergies or autoimmune disorders.

“The idea is that as humans have moved away from farms and an agricultural or hunter-gatherer existence into cities, we have lost contact with organisms that served to regulate our immune system and suppress inappropriate inflammation,” neuroendocrinologist Christopher Lowry, one of the researchers, told CU Boulder Today. “That has put us at higher risk for inflammatory disease and stress-related psychiatric disorders.”

So far, the “vaccine” has only been tested on mice. The mice showed that when immune cells receive the lipid (a fatty acid) from this bacteria, they turn off the inflammation response. This lipid could become the center of drug development that could prevent stress reactions.

If successful, the vaccine could be given to those employed in high-stress situations (like police officers, firefighters or ambulance personnel) and could help stop them from developing PTSD.

However, if the tests move forward, they will raise questions around the potential long-term effects turning off the stress response could have on the brain. We’re still likely a long way off—Lowry estimates it will be another 10 to 15 years before this treatment is available for humans.