Their arguments are based on an understanding of the physiology of fever, body temperature measurement, and fever prevalence in people who transmit COVID-19.

Needing to measure body core temperature raises the first problem with fever screening.

But the forehead skin or inner eye temperatures that infrared thermometers or thermal cameras usually measure in fever screening are not body core temperatures.

Thermal cameras would declare you safe, because your skin temperature is low, but you could be in the most infectious phase of the fever.

So, in addition to not measuring body core temperature well, infrared thermometers are being used to find a high temperature that many people exposed to COVID-19 won't have.