The distance from school/work to home is either long or short, and the good thing is that buses, trains, high-speed trains and planes always make this distance slowly shrink. But due to the epidemic, the distance is not only infinitely longer, but also the last action before going home has changed from buying a ticket to buying a ticket, getting nucleic acid and vaccination. As the epidemic continues today, the precautions for nucleic acid and vaccination have been popularized countless times, but what should we do if we accidentally encounter an unexpected situation?