Severity is a statistic represented by a yellow bar. The higher the Severity of a disease, the easier it will become detected by governments, which will take action and possibly start researching a cure. However, once a cure has started to be developed, even though higher severity makes it more likely that countries will invest more research funding towards developing a cure, since it actually makes the plague harder to cure, severity increases actually generally tend to increase the length of time it takes for the world to successfully develop a cure. Severity also increases the amount of DNA points gained from Red, Bio-hazard Bubbles and infected countries.
Plague types can also increase or decrease Severity. Parasite has a unique ability to reduce overall severity (Symbiosis 1 - 3). Bio-Weapon has unique abilities to raise (and lower) severity, and while most evolutions of the Neurax Worm tend to raise severity, there are symptoms that reduce the overall severity (Adrenergic Constriction and Anxiolytic Infusion). The mutations from Viruses can lead to massive increases in both severity and lethality if left unchecked.