这里有个link: https://www.medicalnewstoday.com/articles/how-long-is-a-person-contagious-with-coronavirus#how-long-are-people-contagious Experts believe that the time from exposure to symptom onset, also known as the incubation period, is 2–14 days. However, symptoms typically appear within 4–5 days of exposure. One 2021 studyTrusted Source included 129 people hospitalized with COVID-19. The median length of time that participants continued to shed the virus was 8 days after first developing symptoms. At 15.2 days, the odds of continuing to shed the virus were less than 5%. These results suggest that shedding may occur for longer than 2 weeks in some people with COVID-19. However, the study only included people who were receiving treatment in a hospital for moderate to severe COVID-19. It is currently not clear whether the result would be the same for people with mild or asymptomatic disease. When are people most contagious? One 2021 reviewTrusted Source suggests that a person with COVID-19 is most contagious in the first week of illness. Therefore, they may be most contagious shortly before and shortly after symptoms appear. For this reason, people should ensure that they isolate immediately if they think that they may have come into contact with the virus or if they have developed symptoms.
但他可以不来训练啊
Experts believe that the time from exposure to symptom onset, also known as the incubation period, is 2–14 days. However, symptoms typically appear within 4–5 days of exposure. One 2021 studyTrusted Source included 129 people hospitalized with COVID-19. The median length of time that participants continued to shed the virus was 8 days after first developing symptoms. At 15.2 days, the odds of continuing to shed the virus were less than 5%. These results suggest that shedding may occur for longer than 2 weeks in some people with COVID-19. However, the study only included people who were receiving treatment in a hospital for moderate to severe COVID-19. It is currently not clear whether the result would be the same for people with mild or asymptomatic disease.
When are people most contagious? One 2021 reviewTrusted Source suggests that a person with COVID-19 is most contagious in the first week of illness. Therefore, they may be most contagious shortly before and shortly after symptoms appear. For this reason, people should ensure that they isolate immediately if they think that they may have come into contact with the virus or if they have developed symptoms.
不可能要求人家不来的，没有任何guideline 说20天后不能恢复正常活动的。只能你自己不去。