We’re now more than seven months into the coronavirus pandemic that has upended the lives of most of Earth’s inhabitants. And while it is true that the scientific community has learned many things about the SARS-CoV-2 virus and the disease it causes, Covid-19, there are also many gaps in our understanding.

One big mystery: Why do some people get very sick and even die from their illness, while other similar people show no symptoms and may not realize they’ve been infected at all? We know some of the big factors that put people at higher risk of having a severe, even fatal, course of disease: being over 60; being overweight or obese; having one or more chronic diseases such as diabetes, cardiovascular disease, kidney or lung disease, and cancer; and  — Black African American, Latino Latinx or Native American.

But might the opposite also be true: Could certain people actually have some type of protection?

A recently published in the journal Nature Reviews Immunology put forth a tantalizing possibility: A large percentage of the population appears to have immune cells that are able to recognize parts of the SARS-CoV-2 virus, and that may possibly be giving them a head start in fighting off an infection. In other words, some people may have some unknown degree of protection. “What we found is that people that had never been exposed to SARS Cov2 … about half of the people had some T-cell reactivity,” co-author of the paper Alessandro Sette from the Center for Infectious Disease and Vaccine Research at La Jolla Institute for Immunology, told CNN.

To understand why that’s important, here’s a little crash course in immunology. The human immune system, which is tasked with keeping you healthy in the face of bacterial, viral, fungal, parasitic and other invaders, has two main components: the innate immune system and the adaptive immune system.

The innate immune system is the very first line of defense. Parts of it include physical barriers like your skin and mucosal membranes, which physically stop invaders from getting in. It also includes certain cells, proteins and chemicals that do things like create inflammation and destroy invading cells.

Read the rest of Dr. Sanjay Gupta and Andrea Kane’s article here at CNN Health