TABLE 1 Stage 3 Study Population (Aged 3-6 Years) by Vaccine Received, Gender, Length of Follow-Up, and Frequency of Nursery School/Kindergarten Attendance Vaccine Received DTaP SB DTaP CB DT Gender   Boys 2089 2093 592   Girls 2128 2122 530   Total 4217 4215 1122 Person-months of follow-up 129 324 130 083 27 611   Average per child (mo) 30.7 30.9 24.6 Proportion months in nursery school/kindergarten   Never 29.9% 29.6% 28.1%   Rarely 2.5% 2.6% 2.6%   Often 13.3% 13.4% 12.0%   Always 54.3% 54.4% 57.3%   Total 100% 100% 100%