Model of disease spread (IMAGE) Princeton University Caption The researchers made modifications to a standard mathematical model of how a disease spreads through a population in which individuals are classified as either susceptible (S), infected (I) or recovered (R). To explore the role of symptomless transmission, the researchers divided the infected (I) compartment into two stages: In I1, individuals' symptoms can range from none (asymptomatic), to mild, to fully symptomatic. In I2, all individuals are fully symptomatic. Credit Chadi Saad-Roy, Princeton University Usage Restrictions Chadi Saad-Roy, Princeton University License Licensed 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.