F2 and COVID-19: The positive rate of anti-FHA IgG antibody in the study population was 20.2% (202/1,000) (≥40 IU/ml) and GMC was 24.94 (95% CI: 22.73–27.16) IU/mL, which were similar to anti-PT-IgG in age, sex, year, and COVID-19 pandemic (Table 2).