A total of 218 participants will be included in this study, and will be randomly assigned 1:1 to the group taking vitamin D2 and the group not taking vitamin D2. Participants in the group taking vitamin D2 orally will receive 200,000 IU of vitamin D2 on the first day of the trial, and again two weeks later (200,000 IU) . The group that will not receive vitamin D2 will not receive any intervention. The whole trial will laste four weeks.

This study is a randomized controlled multicenter clinical trial. Participants who meet the inclusion criteria can be included in this trial after signing informed consent. A total of 218 participants will be included in this study, and will be randomly assigned 1:1 to the group taking vitamin D2 and the group not taking vitamin D2. Participants in the group taking vitamin D2 orally will receive 200,000 IU of vitamin D2 on the first day of the trial, and again two weeks later (200,000 IU) . The group that will not receive vitamin D2 will not receive any intervention. The whole trial will laste four weeks. Throughout the trial, participants' nucleic acid or antigen results, 25(OH)D concentrations, etc., need to be tested.

Inclusion Criteria:

1. Willing to participate in the clinical study and sign the informed consent;
2. Staff members of Peking University Third Hospital, including the hospital headquarters, Capital International Airport Hospital, North Hospital, Beijing Haidian Hospital, Peking University Third Hospital Yanqing Hospital and Peking University Third Hospital Chongli Hospital;
3. Test negative for COVID-19 antigen and have no symptoms related to COVID-19.

Exclusion Criteria:

1. Hospital staff with serious underlying diseases;
2. Pregnant and lactating women;
3. Long-term vegetarians;
4. Long-term chronic diarrhea, history of subtotal gastrectomy, biliary obstructive disease and pancreatic disease.