At the beginning of the outbreak, Hubei Province immediately issued a "health code" to assist in the investigation of the epidemic, and the green code was a "passport" during the epidemic.
Health code is a screening measure, which needs to be completed by people's consciousness. From the beginning, the Health Code only roughly selected healthy people, just to reduce the cost of this epidemic investigation. When the epidemic broke out in China, it was completely unknown how many people had suspected symptoms, and the country could not screen them one by one. In order to let the only resources in China go to the hardest hit areas, this portable verification method was introduced to the public.