Why are travelers to China required to take different tests?

Why are travelers to China required to take different tests?

Entry requirements into China include both a negative PCR swab test and a negative N protein antibody test/IgM antibody serology test.

Vaccination type and status affects the results of the antibody test, due to the proteins being detected by the test. Different antibody tests may be administered, depending on your vaccination type and status:
– Unvaccinated travellers or those vaccinated with Sinovac & Sinopharm: PCR swab test & igM
– Travellers vaccinated with Pfizer-BioTech and Moderna: PCR swab test & N protein antibody test