Decades of research have shown that the human immune response changes in the space environment, but the exact causes and mechanisms of these immune system changes have not yet been determined definitively. Immune system suppression seems to be a common problem in spaceflight, and because some bacteria and other micro-organisms can be more dangerous in the space environment than on Earth, crewmembers may be at greater risk for contracting illnesses and diseases.
Because preliminary research has shown that certain types of bacteria and other micro-organisms may be more dangerous and pose a greater risk of contagion in the space environment, understanding the human immune system's response during spaceflight is an important research priority.
Although most existing research on this topic has been drawn from relatively short-term shuttle missions, HRP research suggests that longer flights may result in a greater degree of immune system disturbance or suppression. As such, the study of human immunology in long-term space flight or space habitation is likely to be an area of research that receives greater attention as NASA prepares for future long-duration missions.