Fig. 1.

Accelerated COVID-19 infection – bypassing the slow and long disease circle of heavily infected individuals by mild or absent sickness behavior. Cytokine-induced sickness behavior, a form of behavioral defense, is a universal adaptive response to infectious pathogens that conserves energy to enhance the efficiency of the immune system. Sickness response includes fever, lethargy/fatigue, depression (or similar signs), irritability, discomfort, pain, nausea, cognitive disturbances including effects on memory and reaction time, and loss of interest in food and drink intake, social interactions and sex. These are triggered in sick individuals, primarily due to a sense of self-preservation and to better cope with pathogens, but evolutionary also to slow the spread of the infection in the community. This is typically achieved by reducing social interactions of sick individuals and further activating in healthy individuals their “behavioral immune system”, resulting in protective behaviors that may favor the avoidance or even expelling of the sick individual (e.g. by maintaining distance or avoiding encounters). Humans are able to infer infection risk from perceptual cues and recognize even subtle signs of sickness in others, including facial, olfactory and vocal changes.