Information has been received from the authors in a published literature article as stated below. HBsAg-positive pregnant women were identified through a program's activities. A staff collected data on maternal demographic and laboratory test results, infant gestational age and birth weight, immunoprophylactic management, and infant serologic outcomes, which were then submitted to the CDC. For the current analysis, data for mother infant pairs reported by the program sites to the CDC from January 2008 through March 2013 were included. The study consisted of an analysis of existing data and was determined by the CDC to be exempt from review by an institutional review board. Measures: Pregnant/postpartum women were eligible for enrollment if they were HBsAg-positive. Perinatal HBV infection was defined as HBsAg positivity in an infant <24 months of age born to an HBsAg-positive woman, regardless of the infant's antibody to hepatitis B surface antigen (anti-HBsAg) test result. Infant infection status was deemed unknown when HBsAg test results were missing or indeterminate. Maternal age at the estimated date of delivery was categorized as follows: <25 years, 25 to 29 years, 30 to 34 years, and 2:35 years; maternal ages <8 years of >54 years were deemed biologically implausible and recoded as missing. Race/ethnicity was analyzed according to 5 categories as reported by the health care provider or case manager. Maternal place of birth and primary language were dichotomized. Maternal laboratory test results included hepatitis B e-antigen (HBeAg), antibody to hepatitis B e-antigen (anti-HBe), and viral load. Results obtained >1 year before the estimated date of delivery or >30 days after the estimated date of delivery were recoded as missing. Unknown and indeterminate values were also recoded as missing. A viral load of 2000 IU/mL was considered equivalent to 10 000 copies/mL and 3.3 log IU/mL. Viral load was dichotomized as 2:2000 IU/mL and <2000 IU/mL in accordance with previous studies defining viral load thresholds. Viral load was recoded as missing when reported in unknown units or in units other than IU/mL, copies/mL, or log IU/mL. Categories of viral load deciles were calculated for viral load values within each category of viral load units (IU/mL, copies/mL, or log IU/mL). Gestational age was calculated on the basis of the number of days between the estimated date of delivery and date of birth. The estimated date of delivery was assumed to correspond to 40 weeks of gestation. Gestational ages calculated as older than 30 days beyond the estimated date of delivery or younger than 150 days before the estimated date of delivery were deemed biologically implausible and recoded as missing. Gestational age was dichotomized as <37 weeks and 2:37 weeks. Infant birth weight was collected dichotomously as either <2000 g or 2:2000 g; unknown infant birth weight was recoded as missing. The timing of administration of the birth dose of HepB vaccine (manufacturer unknown) and HBIG was recoded as missing when either date or time of birth, date or time of HepB vaccine administration, or date or time of HBIG administration were unknown. The administration of HepB vaccine (manufacturer unknown) birth dose of HBIG recorded as 2:120 hours after birth was deemed erroneous and therefore recoded as missing. The timing of administration was dichotomized at less or equal then 12 hours and >12 hours, consistent with ACIP recommendations. Infants were considered to have received 3 HepB vaccine (manufacturer unknown) doses when any date was recorded for a third vaccine dose and were considered to have received <3 HepB vaccine (manufacturer unknown) doses when no date was recorded for a third vaccine dose. Results included that among the 9252 infants for whom HBsAg testing results were available, 100 (1.1%) acquired perinatal HBV infection. The number of HepB vaccine doses was associated with infant infection; 1.1% or 97 of 9207 infants with 2:3 doses, developed infection on the basis of postvaccination testing, compared with 6.7% (3 of 45) of infants with <3 doses (P = .01). Fourteen of 71 infected infants with information weighed <2000 g at birth; 1 of these 14 infants received a fourth vaccine dose. None of the following were significantly associated with perinatal infection: timing of HepB vaccine (manufacturer unknown) birth dose less than 12 vs >12 hours, timing of HBIG administration (less or equal than 12 vs >12 hours), gestational age, or birth weight. Authors discussed that perinatal HBV infection occurred in slightly more than 1% of the 9252 infants born to HBsAg-positive women included in this analysis. Most infected and uninfected infants with birth weights 2:2000 g received ACIP recommended immunoprophylaxis. Before the widespread availability of immunoprophylaxis, the proportion of infants born to HBsAg-positive women acquiring HBV infection was approximately 30% for infants born to HBeAg negative women and 85% for infants born to HBeAg-positive women. On the other hand, found an increased risk of perinatal HBV transmission at younger maternal ages (P = .01). Younger women in the program were more often HBeAg positive than were older women. It has been noted that HBeAg positivity declines during the childbearing years. Studies among HBs-Ag-positive women have reported the prevalence of HBeAg positivity to be between 18.0% and 36.4%. HBeAg positivity was a known risk factor for infectivity. It was plausible that a greater prevalence of HBeAg positivity among younger women accounts for the association between younger maternal age and perinatal transmission. Other have hypothesized that HBeAg positivity and longer labors among younger women could contribute to the increased transmission. Although the majority of perinatal HBV infections are acquired during the birth process, an estimated 5% to 15% of perinatal infections occur from in utero transmission. Authors concluded that timely infant immunoprophylaxis and completion of the 3-dose series prevents most perinatal transmission of HBV and HBV-related morbidity and mortality, as demonstrated by the case management outcomes of infants born to HBsAg-positive pregnant women reported by the program. Additional information has been requested.