<p><strong>BACKGROUND: </strong>A varicella diagnosis or verification of disease history by any healthcare provider is currently accepted for determining evidence of immunity by the Advisory Committee on Immunization Practices (ACIP).</p>

<p><strong>OBJECTIVE: </strong>To examine the accuracy of medical record (MR) documented varicella history as a measure of varicella-zoster virus (VZV) immunity among unvaccinated individuals born after 1980. We also assessed methods to practically implement ACIP guidelines to verify varicella history using medical records.</p>

<p><strong>STUDY DESIGN: </strong>As part of a larger cross-sectional study conducted at three Philadelphia clinics from 2004-2006, we recruited 536 unvaccinated patients aged 5-19 y (birth years: 1985-2001). Varicella history was obtained from three sources: parent/patient interview, any MR documentation (sick and well visits) and MR documentation of a sick visit for varicella. All participants were tested for VZV IgG. For each source and three age groups (5-9, 10-14, 15-19 y old), positive predictive value (PPV) was calculated. Specificity of varicella history was compared between different sources using McNemar's Chi-square.</p>

<p><strong>RESULTS: </strong>Among participants aged 5-9, 10-14 and 15-19 y the PPV for any MR documentation and sick visit diagnosis were 96% and 100%, 92% and 97%, and 99% and 100%, respectively. The specificity for sick visit documentation was higher than any MR documentation and patient/parent recall among all age groups; however, these differences were only statistically significant when comparing sick visit documentation to parent/patient recall for 10-14 y olds.</p>

<p><strong>CONCLUSION: </strong>Sick visit documentation of varicella in the MR is an accurate predictor of varicella seropositivity and useful for confirming disease history among unvaccinated persons (birth years: 1985-2001). This method is a practical way to verify varicella history using the ACIP guidelines.</p>

<p><strong>OBJECTIVE: </strong>We identified maternal, provider, and community predictors among infants for late initiation of immunizations.</p>

<p><strong>METHODS: </strong>We performed a retrospective cohort study of infants born between January 1, 2002, and December 31, 2004, in Philadelphia, Pennsylvania. Primary outcomes were age in days at first office-based immunization and status as a late starter (i.e., initiating office-based immunizations after 90 days of age). Candidate predictors included sociodemographic and prenatal characteristics, immunization provider practice type and size, and neighborhood factors. We performed hierarchical logistic regression and Cox regression models to identify independent predictors for being a late starter and prolonged time to first immunization.</p>

<p><strong>RESULTS: </strong>Of the 65,519 infants from this birth cohort in Philadelphia's immunization registry, 54,429 (88.1%) were included in analysis and 12.6% of these were late starters. Infants whose mothers were younger, received less than five prenatal visits, had less than a high school education, had more than two children, and who smoked cigarettes prenatally were significantly more likely to be late starters. Receiving care at hospital/university-based or public health clinics was also significantly associated with likelihood of being a late starter. Neither distance between infant's residence and practice nor neighborhood socioeconomic indicators was independently associated with the outcomes. Common risk factor profiles based on practice type and four maternal characteristics were found to reliably identify infant risk.</p>

<p><strong>CONCLUSIONS: </strong>Maternal receipt of fewer prenatal care visits, younger maternal age, higher birth order, and receiving care at public health clinics were the strongest predictors of being a late starter and time to first immunization. Risk factor profiles based on information already collected at birth can be used to identify higher-risk infants. Early intervention and potentially partnering with prenatal care providers may be key strategies for preventing underimmunization.</p>