Travel code and health code are both codes obtained by expressing original information with letters and symbols, so the English expression of "travel code" can be expressed by travel code, and the common fixed collocation is "travel code, travel route and travel code status".
Example: The train station needs to enter a trip code.
You need a travel code to enter this railway station.
English expression of health code;
The English of "QR code" is QR code, so the English expression of "health code" is easy to understand. The correct expression is a health QR code or it can be written directly as a health code.
The word code is used because it means "password" when used as a noun. It can neither be replaced by "PIN password" nor be equated with "password password /kouling", while code emphasizes the use of "letters and symbols" to represent the code obtained from the original information.
He entered the security code.
He entered the password into the computer.
The person with the wrong area code can't get through.
When the caller dials the wrong area code, the call cannot be answered.
For example, the "area code" of a country or region is "area code" or "dialing code" and so on. For another example, in some spy movies, the "code name" used by agents to perform secret tasks is usually called "a code name".
Sometimes it is not enough to have a "health code", because out of your city, the "health code" may not be used, because every region is different, and then the "tourist card" will come in handy. It is universal, and it is used to see where a person has been and understand his travel track.