After the outbreak of the COVID-19 epidemic, China has formed a complete prevention and control system. One of the screening measures is to scan the "health code", which represents the prevention and control level of the holder and is generally divided into three colors: green, yellow and red. Green stands for everything is normal, yellow stands for intermediate prevention and control needs, generally for abnormal body temperature/fever, dry cough, diarrhea and other suspected symptoms/need to be isolated at home, red stands for advanced prevention and control needs, generally for confirmed diagnosis, suspected cases, positive nucleic acid test, asymptomatic infection/close contacts or close contacts/living history in medium and high-risk areas, etc. Basically, people with the above control measures need to be isolated.
At present, all countries and provinces have health codes, and some cities also have their own health codes. Each health code has an independent programming and operating system, and its operation mode and logical relationship are different. According to the requirements of air defense in different periods, the prevention and control measures for green and yellow QR codes are different. However, if it has been verified accurately, the red and health codes generally need to take centralized isolation observation and higher control measures for the holders immediately. In some places, the management of health codes is not clear, or individuals are supported to fill in information, so there is an inaccurate coding color, which needs to be checked by the prevention and control department or the Big Data Administration.