I have a biology degree, and a particular interest in Immunology and I have no idea what actually went from 27 to 0. It's not white blood cells, which would be the immediate thought.,(reply>), WELP it's been removed from wikipedia by now due to the complete lack of sources and units,(reply>), Resistonses,(reply>), Maybe it was the amount of new infections.<br>When you're sitting in a glass box in a cave, there is hardly anything around to get infected with.,(reply>), immunity index or some made up thing? (they used to make up and claim a lot of things back then),(reply>), It sounds like some manner of in-house test score that measures overall immune system responsiveness based on all of the specific test factors.  I'm no immunologist, but I am an engineer, if significantly less qualified than the NASA ones who would be involved in this test, and they'd probably want an overall score that summarizes the immune system's ability to handle things.  Something along the lines of working out a constitution score for a D&amp;D character sheet representing them, that sort of thing.  Engineers like summarized, digestible data up front and access to details when called for.