Objectives: In 2019, the Council of State and Territorial Epidemiologists ratified a multitiered standardized surveillance case definition (SSCD) for neonatal abstinence syndrome (NAS) to minimize variability in definitions across states. This evaluation of the tier 1 NAS SSCD aimed to identify common challenges and opportunities for enhancement to support consistent implementation of the definition. Methods: This mixed-methods analysis consisted of 3 virtual focus groups in March 2021 with site principal investigators, medical record abstractors, and data analysts (1 focus group each) from 4 jurisdictions piloting the tier 1 NAS SSCD. We analyzed focus group transcripts to create a codebook. We collected written reports in February 2022 from the 4 jurisdictions, conducted thematic analysis of focus group transcripts and written reports to identify themes, and collected surveillance data on infants identified with NAS born from January 2020 through December 2021 from the pilot sites. We analyzed surveillance data to further inform identified themes. We examined agreement among tier 1 classifications assigned independently by each pilot site and the Centers for Disease Control and Prevention to cases of NAS. Results: Three major themes emerged in the data: challenges abstracting data on withdrawal signs from the medical record, difficulty determining the time frame of prenatal substance exposure, and challenges assigning case classifications. In a comparison of tier 1 classifications assigned by the Centers for Disease Control and Prevention and the sites, 82.1% of cases in the dataset were concordant. Conclusions: We identified several opportunities to modify the SSCD to promote consistency and ease implementation across jurisdictions. Promoting consistent implementation supports comparability of NAS incidence estimates across jurisdictions, evaluation of prevention efforts, and allocation of resources to support families. © 2024, Association of Schools and Programs of Public Health.

BACKGROUND: We provide updated crude and adjusted prevalence estimates of major birth defects in the United States for the period 2016-2020. METHODS: Data were collected from 13 US population-based surveillance programs that used active or a combination of active and passive case ascertainment methods to collect all birth outcomes. These data were used to calculate pooled prevalence estimates and national prevalence estimates adjusted for maternal race/ethnicity for all conditions, and maternal age for trisomies and gastroschisis. Prevalence was compared to previously published national estimates from 1999 to 2014. RESULTS: Adjusted national prevalence estimates per 10,000 live births ranged from 0.63 for common truncus to 18.65 for clubfoot. Temporal changes were observed for several birth defects, including increases in the prevalence of atrioventricular septal defect, tetralogy of Fallot, omphalocele, trisomy 18, and trisomy 21 (Down syndrome) and decreases in the prevalence of anencephaly, common truncus, transposition of the great arteries, and cleft lip with and without cleft palate. CONCLUSION: This study provides updated national estimates of selected major birth defects in the United States. These data can be used for continued temporal monitoring of birth defects prevalence. Increases and decreases in prevalence since 1999 observed in this study warrant further investigation.

OBJECTIVE: To evaluate the hypothesis that childhood survival for individuals with Down syndrome (DS) and congenital heart defects (CHDs) has improved in recent years, approaching survival of those with DS without CHDs. STUDY DESIGN: Individuals with DS born 1979-2018 were identified through the Metropolitan Atlanta Congenital Defects Program, a population-based birth defects surveillance system administered by the Centers for Disease Control and Prevention. Survival analysis was performed to evaluate predictors of mortality for those with DS. RESULTS: The cohort included 1,671 individuals with DS; 764 had associated CHDs. Five-year survival in those with DS with CHD improved steadily among individuals born in the 1980s through the 2010s (85% to 93%, p=0.01) but remained stable (96% to 95%, p=0.97) in those with DS without CHDs. The presence of a CHD was not associated with mortality through 5 years of age for those born 2010 or later (hazard ratio 2.63 [95% confidence interval 0.95 - 8.37]). In multivariable analyses, atrioventricular septal defects were associated with early (<1 year) and late (>5 year) mortality, while ventricular septal defects were associated with intermediate (1-5 years) mortality and atrial septal defects with late mortality, when adjusting for other risk factors. CONCLUSIONS: The gap in five-year survival between children with DS with and without CHDs has improved over the last four decades. Survival after 5 years remains lower for those with CHDs, although longer follow-up will be needed to determine if this difference lessens for those born in the more recent years.

The emergence of birth defects programs in the United States accelerated in the 1970s and 1980s due to recognition that the use of the drug thalidomide during pregnancy resulted in fetal abnormalities (McBride, 1961; Smithells, 1962) and concerns around environmental exposures, such as Agent Orange exposure during the Vietnam War (Erickson et al., 1984). These experiences shaped the mission of many birth defect programs to focus on the surveillance of fetuses/infants affected by birth defects to monitor prevalence, identify and respond to clusters, and explore the epidemiology of birth defects as early warning systems to identify potential teratogens. This work helped identify additional risk factors for birth defects, support primary prevention opportunities, such as folic acid fortification and supplementation for neural tube defect prevention, and enabled evaluations of the success of those efforts (Harris et al., 2017).

BACKGROUND: The Standards for Adult Immunization Practice (Standards), revised in 2014, emphasize that adult-care providers assess vaccination status of adult patients at every visit, recommend vaccination, administer needed vaccines or refer to a vaccinating provider, and document vaccinations administered in state/local immunization information systems (IIS). Providers report numerous systems- and provider-level barriers to vaccinating adults, such as billing, payment issues, lower prioritization of vaccines due to competing demands, and lack of information about the use and utility of IIS. Barriers to vaccination result in missed opportunities to vaccinate adults and contribute to low vaccination coverage. Clinicians' (physicians, physician assistants, nurse practitioners) and pharmacists' reported barriers to assessment, recommendation, administration, referral, and documentation, provider vaccination practices, and perceptions regarding their adult patients' attitudes toward vaccines were evaluated. METHODS: Data from non-probability-based Internet panel surveys of U.S. clinicians (n=1714) and pharmacists (n=261) conducted in February-March 2017 were analyzed using SUDAAN. Weighted proportion of reported barriers to assessment, recommendation, administration, referral, and documentation in IIS were calculated. RESULTS: High percentages (70.0%-97.4%) of clinicians and pharmacists reported they routinely assessed, recommended, administered, and/or referred adults for vaccination. Among those who administered vaccines, 31.6% clinicians' and 38.4% pharmacists' submitted records to IIS. Reported barriers included: (a) assessment barriers: vaccination of adults is not within their scope of practice, inadequate reimbursement for vaccinations; (b) administration barriers: lack of staff to manage/administer vaccines, absence of necessary vaccine storage and handling equipment and provisions; and (c) documentation barriers: unaware if state/city has IIS that includes adults or not sure how their electronic system would link to IIS. CONCLUSION: Although many clinicians and pharmacists reported implementing most of the individual components of the Standards, with the exception of IIS use, there are discrepancies in providers' reported actual practices and their beliefs/perceptions, and barriers to vaccinating adults remain.

BACKGROUND: Reminders for influenza vaccination improve influenza vaccination coverage. The purpose of this study was to describe the receipt of reminders for influenza vaccination during the 2011-12 influenza season among U.S. adults. METHODS: We analyzed data from the March 2012 National Flu Survey (NFS), a random digit dial telephone survey of adults in the United States. Relative to July 1, 2011, respondents were asked if they received a reminder for influenza vaccination and the source and type of reminder they received. The association with reminder receipt and demographic variables, and the association between influenza vaccination coverage and receipt of reminders were also examined. RESULTS: Of adults interviewed, 17.2% reported receiving a reminder since July 1, 2011. More than half (65.2%) of the reminders were sent by doctor offices. Hispanics and non-Hispanic blacks were more likely than non-Hispanic whites to report receiving a reminder. Adults who reported having a usual health care provider, health insurance, or a high-risk condition were more likely to report receiving reminders than the respective reference group. Adults reporting receipt of reminders were 1.15 times more likely (adjusted prevalence ratio, 95% CI: 1.06-1.25) to report being vaccinated for influenza than adults reporting not receiving reminders. CONCLUSIONS: Differences exist in receipt of influenza vaccination reminders among adults. Reminders are important tools to improve adult influenza vaccination coverage. Greater use of reminders may lead to higher rates of adult influenza vaccination coverage and reductions in influenza-related morbidity. This article is protected by copyright. All rights reserved.

In 2016, 55 jurisdictions in 49 states and six cities in the United States used immunization information systems (IISs) to collect and manage immunization data and support vaccination providers and immunization programs. To monitor progress toward achieving IIS program goals, CDC surveys jurisdictions through an annual self-administered IIS Annual Report (IISAR). Data from the 2013-2016 IISARs were analyzed to assess progress made in four priority areas: 1) data completeness, 2) bidirectional exchange of data with electronic health record systems, 3) clinical decision support for immunizations, and 4) ability to generate childhood vaccination coverage estimates. IIS participation among children aged 4 months through 5 years increased from 90% in 2013 to 94% in 2016, and 33 jurisdictions reported ≥95% of children aged 4 months through 5 years participating in their IIS in 2016. Bidirectional messaging capacity in IISs increased from 25 jurisdictions in 2013 to 37 in 2016. In 2016, nearly all jurisdictions (52 of 55) could provide automated provider-level coverage reports, and 32 jurisdictions reported that their IISs could send vaccine forecasts to providers via Health Level 7 (HL7) messaging, up from 17 in 2013. Incremental progress was made in each area since 2013, but continued effort is needed to implement these critical functionalities among all IISs. Success in these priority areas, as defined by the IIS Functional Standards (1), bolsters clinicians' and public health practitioners' ability to attain high vaccination coverage in pediatric populations, and prepares IISs to develop more advanced functionalities to support state/local immunization services. Success in these priority areas also supports the achievement of federal immunization objectives, including the use of IISs as supplemental sampling frames for vaccination coverage surveys like the National Immunization Survey (NIS)-Child, reducing data collection costs, and supporting increased precision of state-level estimates.

OBJECTIVE: Coverage with rotavirus vaccine among US children has been lower compared to that with other routine childhood vaccines. Our objectives were to examine rotavirus vaccine (RV) uptake over time compared to other routine vaccinations, ages at administration, and quantitate potential missed opportunities for RV receipt. METHODS: We analyzed data from 6 Immunization Information System (IIS) Sentinel Sites, which represent approximately 10% of the United States (US) pediatric population. Among infants aged 5 months, we compared uptake of 1 dose of RV, to that of Diphtheria, Tetanus, and acellular Pertussis (DTaP) and pneumococcal conjugate vaccine (PCV), for each quarter during 2006-2013. We used data from infants in the 2012 birth cohort to examine RV receipt in more detail. RESULTS: Among infants aged 5months, the average site coverage with 1 dose of RV reached 78% in 2010 and subsequently stayed steady at 79-81% through 2013. The average difference between 1 dose DTaP coverage and RV coverage remained between about 6 and 8 percentage points during mid-2012 through 2013. Infants born in 2012 received RV doses closely in line with the timing recommended by the ACIP. Approximately one-third of the difference in coverage between 1 dose of DTaP and 1 dose of RV among infants could be due to the maximum age restriction of the first RV dose. The other two-thirds of the difference appears to have been a result of potential missed opportunities for starting the RV series--these infants received another routine immunization when age eligible to receive RV dose 1, but did not receive RV. CONCLUSION: Uptake with RV during infancy remains below that of other routine vaccines. Understanding the barriers to administration of RV among age-eligible infants could help improve vaccine coverage.

BACKGROUND: Children aged 6 months through 8 years may require two doses of influenza vaccine for adequate immune response against the disease. However, poor two-dose compliance has been reported in the literature. METHODS: We analyzed data for >2.6million children from six immunization information system (IIS) sentinel sites, and assessed full vaccination coverage and two-dose compliance in the 2010-2015 influenza vaccination seasons. Full vaccination was defined as having received at least the recommended number of influenza vaccine doses (one or two), based on recommendations from the Advisory Committee on Immunization Practices. Two-dose compliance was defined as the percentage of children during each season who received at least two doses of influenza vaccine among those who required two doses and initiated the series. RESULTS: Across seasons, 1-dose influenza vaccination coverage was mainly unchanged among 6-23montholds (range: 60.9-66.6%), 2-4yearolds (range: 44.8-47.4%), and 5-8yearolds (range: 34.5-38.9%). However, full vaccination coverage showed increasing trends from 2010-11 season to 2014-15 season (6-23months: 43.0-46.5%; 2-4yearolds: 26.3-39.7%; 5-8yearolds, 18.5-33.9%). Across seasons, two-dose compliance remained modest in children 6-23months (range: 63.3-67.6%) and very low in older children (range: 11.6-18.7% in children 2-4yearsand6.8-13.3% in children 5-8years). In the 2014-15 season, among children who required and received 2 doses, only half completed the two-dose series before influenza activity peaked. CONCLUSIONS: Improved messaging of the two-dose influenza vaccine recommendations is needed for providers and parents. Providers are encouraged to determine a child's eligibility for two doses of influenza vaccine using the child's vaccination history, and to vaccinate children early in the season so that two-dose series are completed before influenza peaks.

INTRODUCTION: Immunization information systems (IISs) are highly effective for increasing vaccination rates but information about how primary care physicians use them is limited. METHODS: Pediatricians, family physicians (FPs), and general internists (GIMs) were surveyed by e-mail and mail from January 2015 to April 2015 from all states with an existing IIS. Providers were recruited to be representative of national provider organization memberships. Multivariable log binomial regression examined factors associated with IIS use (October 2015-April 2016). RESULTS: Response rates among pediatricians, FPs, and GIMs, respectively, were 75% (325/435), 68% (310/459), and 63% (272/431). A proportion of pediatricians (5%), FPs (14%), and GIMs (48%) did not know there was a state/local IIS; 81%, 72%, and 27% reported using an IIS (p<0.0001). Among those who used IISs, 64% of pediatricians, 61% of FPs, and 22% of GIMs thought the IIS could tell them a patient's immunization needs; 22%, 29%, and 51% did not know. The most frequently reported major barriers to use included the IIS not updating the electronic medical record (29%, 28%, 35%) and lack of ability to submit data electronically (22%, 27%, 31%). Factors associated with lower IIS use included FP (adjusted risk ratio=0.85; 95% CI=0.75, 0.97) or GIM (adjusted risk ratio=0.33; 95% CI=0.25, 0.42) versus pediatric specialty and older versus younger provider age (adjusted risk ratio=0.96; 95 CI%=0.94, 0.98). CONCLUSIONS: There are substantial gaps in knowledge of IIS capabilities, especially among GIMs; barriers to interoperability between IISs and electronic medical records affect all specialties. Closing these gaps may increase use of proven IIS functions including decision support and reminder/recall.

Annual influenza vaccination is recommended for everyone ≥6 months in the U.S. During the 2013-14 influenza season, in addition to trivalent influenza vaccines, quadrivalent vaccines were available, protecting against two influenza A and two influenza B viruses. We analyzed 1,976,443 immunization records from six sentinel sites to compare influenza vaccine usage among children age 6 months-18 years. A total of 983,401 (49.8%) influenza vaccine doses administered were trivalent and 920,333 (46.6%) were quadrivalent (unknown type: 72,709). Quadrivalent vaccine administration varied by age and was least frequent among those <2 years of age.

The use of electronic health information to support clinical and public health services has increased in recent years. One of the leaders in advancing this field is immunization information systems (IISs). Immunization information systems are confidential, population-based, computerized databases that record all immunization doses administered by participating providers to persons residing within a given geopolitical area. They began to be established in the 1970s mostly as local or regional systems that were intended primarily to consolidate childhood vaccination histories to support immunization delivery at the point of pediatric clinical care. In recent years, IISs have evolved to utilize emerging interfacing technology and industry standards to facilitate the exchange of information among a more diverse set of clinical and public health immunization partners within and outside their respective jurisdictions. They have developed a multitude of functions and features that have made them essential components of immunization service delivery and management to clinicians, public health, and other stakeholders such as schools and health plans for individuals of all ages. With the growing exchange of electronic health information and the increased demand on IIS data and services, IISs face new opportunities and challenges to ensure the complete, accurate, and timely capture and availability of immunization information.

The Advisory Committee on Immunization Practices (ACIP) recommends annual influenza vaccination for all persons in the United States aged ≥6 months. On June 25, 2014, ACIP preferentially recommended live attenuated influenza vaccine (LAIV) for healthy children aged 2-8 years [1]. Little is known about national LAIV uptake. To determine uptake of LAIV relative to inactivated influenza vaccine, we analyzed vaccination records from six immunization information system sentinel sites (approximately 10% of US population). LAIV usage increased over time in all sites. Among children 2-8 years of age vaccinated for influenza, exclusive LAIV usage in the collective sentinel site area increased from 20.1% (2008-09 season) to 38.0% (2013-14). During 2013-14, at least half of vaccinated children received LAIV in Minnesota (50.0%) and North Dakota (55.5%). Increasing LAIV usage suggests formulation acceptability, and this preexisting trend offers a favorable context for implementation of ACIP's preferential recommendation.

CONTEXT: A recent systematic review found that use of an immunization information system (IIS) is an effective intervention to increase vaccination rates. The purpose of this review was to evaluate costs and benefits associated with implementing, operating, and participating with an IIS. The speed of technology change has had an effect on costs and benefits of IIS and is considered in this review. EVIDENCE ACQUISITION: An economic evaluation for IIS was conducted using methods developed for Community Guide systematic reviews. The literature search covered the period from January 1994 to March 2012 and identified 12 published articles and 2 government reports. EVIDENCE SYNTHESIS: Most studies involving cost data evaluated (1) system costs of building an IIS and (2) cost of exchanging immunization data; most economic benefits focused on administrative efficiency. CONCLUSIONS: A major challenge to evaluating a technology-based intervention is the evolution that comes with technology improvements and advancements. Although the cost and benefit data may be less applicable today due to changes in system technology, data exchange methods, availability of vendor support, system functionalities, and scope of IIS, it is likely that more up-to-date estimates and comprehensive estimates of benefits would support the findings of cost savings in this review. More research is needed to update and address limitations in the available evidence and to enable assessment of economic costs and benefits of present-day IIS.

CONTEXT: Immunizations are the most effective way to reduce incidence of vaccine-preventable diseases. Immunization information systems (IISs) are confidential, population-based, computerized databases that record all vaccination doses administered by participating providers to people residing within a given geopolitical area. They facilitate consolidation of vaccination histories for use by health care providers in determining appropriate client vaccinations. Immunization information systems also provide aggregate data on immunizations for use in monitoring coverage and program operations and to guide public health action. EVIDENCE ACQUISITION: Methods for conducting systematic reviews for the Guide to Community Preventive Services were used to assess the effectiveness of IISs. Reviewed evidence examined changes in vaccination rates in client populations or described expanded IIS capabilities related to improving vaccinations. The literature search identified 108 published articles and 132 conference abstracts describing or evaluating the use of IISs in different assessment categories. EVIDENCE SYNTHESIS: Studies described or evaluated IIS capabilities to (1) create or support effective interventions to increase vaccination rates, such as client reminder and recall, provider assessment and feedback, and provider reminders; (2) determine client vaccination status to inform decisions by clinicians, health care systems, and schools; (3) guide public health responses to outbreaks of vaccine-preventable disease; (4) inform assessments of vaccination coverage, missed vaccination opportunities, invalid dose administration, and disparities; and (5) facilitate vaccine management and accountability. CONCLUSIONS: Findings from 240 articles and abstracts demonstrate IIS capabilities and actions in increasing vaccination rates with the goal of reducing vaccine-preventable disease.

In 2007, the Advisory Committee on Immunization Practices (ACIP) recommended a routine second dose of varicella vaccine for children at age 4-6 years, in addition to the first dose given at age 12-15 months. One strategy recommended for increasing varicella vaccination coverage is a school entry requirement of proof of varicella immunity. To determine the extent of implementation of the routine 2-dose varicella vaccination program, the number of states with a 2-dose varicella vaccination elementary school entry requirement in 2012 was compared with the number in 2007, and 2-dose varicella vaccination coverage during 2006 was compared with coverage in 2012 among children aged 7 years, using data from six Immunization Information System (IIS) sentinel sites. The number of states (including the District of Columbia) with a 2-dose varicella vaccination elementary school entry requirement increased from four in 2007 to 36 in 2012. Two-dose varicella vaccination coverage levels among children aged 7 years in the six IIS sentinel sites increased from a range of 3.6%-8.9% in 2006 to a range of 79.9%-92.0% in 2012 and were approaching the levels of 2-dose measles, mumps, and rubella (MMR) coverage, which had a range of 81.9%-94.0% in 2012. These increases suggest substantial progress in implementing the routine 2-dose varicella vaccination program in the first 6 years since its recommendation by ACIP. Wider adoption of 2-dose varicella vaccination school entry requirements might help progress toward the Healthy People 2020 target of 95% of kindergarten students having received 2 doses of varicella vaccine.

PROBLEM/CONDITION: Substantial improvement in annual influenza vaccination of recommended groups is needed to reduce the health effects of influenza and reach Healthy People 2020 targets. No single data source provides season-specific estimates of influenza vaccination coverage and related information on place of influenza vaccination and concerns related to influenza and influenza vaccination. REPORTING PERIOD: 2007-08 through 2011-12 influenza seasons. DESCRIPTION OF SYSTEMS: CDC uses multiple data sources to obtain estimates of vaccination coverage and related data that can guide program and policy decisions to improve coverage. These data sources include the National Health Interview Survey (NHIS), the Behavioral Risk Factor Surveillance System (BRFSS), the National Flu Survey (NFS), the National Immunization Survey (NIS), the Immunization Information Systems (IIS) eight sentinel sites, Internet panel surveys of health-care personnel and pregnant women, and the Pregnancy Risk Assessment and Monitoring System (PRAMS). RESULTS: National influenza vaccination coverage among children aged 6 months-17 years increased from 31.1% during 2007-08 to 56.7% during the 2011-12 influenza season as measured by NHIS. Vaccination coverage among children aged 6 months-17 years varied by state as measured by NIS. Changes from season to season differed as measured by NIS and NHIS. According to IIS sentinel site data, full vaccination (having either one or two seasonal influenza vaccinations, as recommended by the Advisory Committee on Immunization Practices for each influenza season, based on the child's influenza vaccination history) with up to two recommended doses for the 2011-12 season was 27.1% among children aged 6 months-8 years and was 44.3% for the youngest children (aged 6-23 months). Influenza vaccination coverage among adults aged ≥18 years increased from 33.0% during 2007-08 to 38.3% during the 2011-12 influenza season as measured by NHIS. Vaccination coverage by age group for the 2011-12 season as measured by BRFSS was <5 percentage points different from NHIS estimates, whereas NFS estimates were 6-8 percentage points higher than BRFSS estimates. Vaccination coverage among persons aged ≥18 years varied by state as measured by BRFSS. For adults aged ≥18 years, a doctor's office was the most common place for receipt of influenza vaccination (38.4%, BRFSS; 32.5%, NFS) followed by a pharmacy (20.1%, BRFSS; 19.7%, NFS). Overall, 66.9% of health-care personnel (HCP) reported having been vaccinated during the 2011-12 season, as measured by an Internet panel survey of HCP, compared with 62.4%, as estimated through NHIS. Vaccination coverage among pregnant women was 47.0%, as measured by an Internet panel survey of women pregnant during the influenza season, and 43.0%, as measured by BRFSS during the 2011-12 influenza season. Overall, as measured by NFS, 86.8% of adults aged ≥18 years rated the influenza vaccine as very or somewhat effective, and 46.5% of adults aged ≥18 years believed their risk for getting sick with influenza if unvaccinated was high or somewhat high. INTERPRETATION: During the 2011-12 season, influenza vaccination coverage varied by state, age group, and selected populations (e.g., HCP and pregnant women), with coverage estimates well below the Healthy People 2020 goal of 70% for children aged 6 months-17 years, 70% for adults aged ≥18 years, and 90% for HCP. PUBLIC HEALTH ACTIONS: Continued efforts are needed to encourage health-care providers to offer influenza vaccination and to promote public health education efforts among various populations to improve vaccination coverage. Ongoing surveillance to obtain coverage estimates and information regarding other issues related to influenza vaccination (e.g., knowledge, attitudes, and beliefs) is needed to guide program and policy improvements to reduce morbidity and mortality associated with influenza by increasing vaccination rates. Ongoing comparisons of telephone and Internet panel surveys with in-person surveys such as NHIS are needed for appropriate interpretation of data and resulting public health actions. Examination of results from all data sources is necessary to fully assess the various components of influenza vaccination coverage among different populations in the United States.

Children aged <9 years may require two doses of influenza vaccine to achieve an adequate immune response to protect against the disease. We analyzed data for >2 million children in each influenza season from 2007 to 2012 from eight Immunization Information System Sentinel Sites to assess trends in two-dose compliance. Compliance was calculated by influenza season, age group, and influenza vaccination history. Two-dose compliance increased from 49% to 60% among 6-23 month olds from 2007 to 2012; no increase was observed for 2-4 or 5-8 year olds. In each season, compliance was 3-12 times higher among 6-23 month olds compared to older children and was two times higher among influenza vaccine naive children compared to previously vaccinated children. Improved messaging for providers and parents about the importance of the two-dose recommendation, about which children are eligible for two doses, and provider access to complete influenza vaccination histories for all children are needed.

Recommendations for routine vaccination of all children aged 6 to 23 months and 24 to 59 months with seasonal influenza vaccine were first published by the Advisory Committee for Immunization Practices (ACIP) in 2004 and 2006, respectively.1 Vaccine effectiveness and immunogenicity studies have shown that administration of only 1 influenza vaccine dose in the first year of vaccination conveys suboptimal protection.2-4 Prior to the 2007-2008 influenza season, children aged less than 9 years were recommended to receive 2 doses in their first year of vaccination.1 Two-dose vaccination recommendations were expanded for the 2007-2008 season to include children who received only 1 dose for the first time in the previous season.1 | Monitoring 2-dose compliance for influenza vaccination is important for evaluating vaccination efforts and developing innovative strategies to improve coverage. A limited number of studies have assessed 2-dose compliance in children. The Vaccine Safety Datalink Project, which includes data from 8 health maintenance organizations, reported that 2-dose compliance among children aged 6 to 23 months ranged from 29% to 54% during the 2001-2002, 2002-2003, and 2004-2005 seasons.5 Rates were lower among children aged 2 to 8 years (12%-24%). Data from the National Immunization Survey showed that only 11% of vaccine naïve children aged 6 to 23 months received both doses during the 2005-2006 influenza season.6 And, a recent study using private pediatric practice data from the 2007-2008 and 2008-2009 seasons found 2-dose compliance rates of 49.9% to 58.7% among 6- to 23-month-olds and 37.6% to 45.2% among 24- to 59-month-olds.7 | Because 2-dose compliance for immunization vaccination has not been assessed using population-based data since 2-dose vaccination recommendations changed for the 2007-2008 season, data from the Immunization Information System Sentinel Site Project were used to assess compliance among children aged 6 to 59 months during the 2007-2008 season and to determine if influenza vaccination history was associated with completion of 2 doses.