Statistical analysis
Data was entered into Microsoft Excel (Microsoft, WA) and statistics were computed within the software. Binomial Exact tests and Wilson’s Confidence Intervals were used to determine if the cohort’s seropositivity was significantly different than the general population’s rate. The general population’s seropositivity rates were chosen from long-term studies of antibody persistence. Seropositivity for measles, mumps, and rubella were set at 95%, 74%, and 100% respectively as found by Davidkin et. al, 15-20 years after vaccination.14 Rubella seropositivity was adjusted to 99% to avoid divide by zero errors within Excel. Varicella seropositivity was set to 99% based on the results of Vessey et al. and Watson et al. 15,16who took titers at one and six years respectively. Although Vessey et al. found 100% seropositivity at one year, a rate of 99% eliminates divide by zero errors in Excel. Tetanus seropositivity was set at 85.8% as found by Borella-Venturini et al.17 for those who received <5 doses. Not all subjects received the 4th and 5th doses of the DTaP vaccine and therefore this value represents a more accurate representation of the cohort. Hepatitis B had a greater literature base from which to choose a seropositivity rate. In following the CDC citations, seropositivity was set at 66% (15-year mark) as reported by McMahon et al.18