F2 and tetanus: A study of 6- to 8-year-old children in China who had completed 4 doses of co-purified  diphtheria, tetanus, and whole cell pertussis combined vaccine (DTwP) showed the following pre-booster seropositivity rates: 5.6% for anti-PT, 40.1% for anti-FHA, 72.2% for anti-DT, and 83.3% for anti-TT, also demonstrating high variability in seropositivity rates between different antigens (5%–83%)42.