There is no medical examination requirement for immigrants in the United States, which means it is impossible to enter the United States without a medical examination.
However, there are regulations in China that 0. 1% of people will have their health certificates randomly checked when they return to China (the official statement says so). If you don't have a valid health certificate within one year, you need to go to the local entry-exit immunization department for a physical examination on the day of entry before you can approve normal entry. In addition, one-thousandth of the candidates are generally people who have returned from epidemic areas.