Illustration of model finding (IMAGE) University of Washington Caption This illustration represents the core theory in a new modeling study led by the University of Washington: The circles represent the immune system's aging, in which its ability to make new immunity cells remains constant until a person (represented by the human figures) reaches middle-age or older and then falls off significantly. The central blue figure represents an immune system T cell that attacks the virus. Credit Michele Kellett and James Anderson/University of Washington Usage Restrictions Credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.