Children with neurologic and neurodevelopmental disorders are at high risk for influenza-associated complications, including respiratory failure and death.1 These children accounted for one-third of reported influenza-associated deaths in the United States from 2004 to 2012.2 Furthermore, their overall rates of respiratory infection hospitalizations were estimated to be 5- to 7-fold greater than the general pediatric population; estimated rates of in-hospital death from respiratory infections were 20- to 55-fold greater.3 The increased risk is due to impaired mobility, decreased muscle tone, diminished ability to handle secretions and mechanical factors that impair pulmonary function.1,3
Annual influenza vaccination, recommended for children with neurologic and neurodevelopmental disorders since 2005, and for all children ≥6 months of age since 2008, is the best available method of preventing influenza virus infections.4 The rarity of neurologic disorders makes population-based estimates of vaccination coverage in children with neurologic disorders challenging, and influenza vaccination in this population is not well described. Furthermore, given high influenza transmission rates among family members, ensuring vaccination of siblings is recommended to provide additional protection for vulnerable children.4 However, whether siblings of these high-risk children are more likely to be vaccinated than the general pediatric population is unknown.
We analyzed a deidentified commercial insurance claims database over 8 years, from July 2006 to June 2014 (MarketScan Commercial Claims and Encounters; Truven Health Analytics: Ann Arbor, Michigan). This database collects individual-level insurance claims data on approximately 40 million adults and children annually. We reported vaccination coverage rates in children with neurologic disorders, their siblings and the general pediatric population. Data were divided into 12-month periods (July to June). Children could be included in multiple seasons, and data from children identified in each season were analyzed separately.
We included children 1–17 years of age as of July 1 who were continuously enrolled throughout that season and were also enrolled for ≥1 month in the preceding 12 months. As previously described, children were identified as having a neurologic disorder if they had ≥1 inpatient or outpatient visit during that time period with an International Classification of Diseases, 9th revision, billing code identifying them as having a neurologic disorder, including muscular dystrophy, chromosomal anomalies, metabolic diseases, motor neuron diseases, central nervous system degenerative diseases, cerebral palsy, spina bifida, other central nervous system anomalies, traumatic brain injury and epilepsy (Appendix 1, Supplemental Digital Content 1, https://links.lww.com/INF/C984).3 Children could be identified as having more than 1 neurologic disorder.
Siblings were identified by a code linking them to the person under whose insurance they were covered; we assumed that children with shared codes were siblings. As a comparison group, we selected a general pediatric sample from the same database. Because of the database’s large size, we randomly selected 10% of continuously enrolled children in a given season to comprise the general pediatric sample.
Pharmacy or outpatient procedure codes indicated influenza vaccination. We did not examine whether children were fully vaccinated per Immunization Practices Advisory Committee guidelines5; if a single vaccination code was identified, the child was considered vaccinated. In the 2009–2010 season, this included either the seasonal trivalent influenza vaccine or monovalent influenza A(H1N1)pdm09 vaccine.
We identified 184,460 unique children with neurologic disorders, representing 324,022 person-years, 204,966 siblings (357,151 person-years) and 4,697,486 children (5,523,202 person-years) for the general pediatric sample. Subject characteristics are shown in Appendix 2, Supplemental Digital Content 1, https://links.lww.com/INF/C984. The most commonly identified disorder was epilepsy, followed by cerebral palsy; among those identified with epilepsy, children representing 136,240 (74%) person-years had isolated epilepsy, while the remaining 26% had epilepsy and another neurologic disorder. Children with neurologic disorders had a mean of 1.1 siblings identified.
Among children with neurologic disorders, 34.6% were vaccinated, a higher proportion when compared with either siblings (28.1%) or the general pediatric population (23.8%; P < 0.01). The proportion vaccinated was highest among those with muscular dystrophy (48.6%) and lowest among those with epilepsy (30.9%).
The proportion of children vaccinated steadily increased over the course of the study in all groups (P < 0.01), with a single anomalous year during 2009–2010, in which either seasonal influenza vaccine or the influenza A(H1N1)pdm09 monovalent vaccine was considered as being vaccinated (Fig. 1A). Coverage declined in the 2010–2011 season among children with neurologic disorders and their siblings, but not among the general pediatric population, and increased in all 3 groups in subsequent seasons. Among children with neurologic disorders, coverage increased from 22.4% in 2006–2007 to 42.3% in 2013–2014. Vaccination coverage decreased with age, and was lowest among children 10–17 years of age in all 3 groups (Fig. 1B); among these children in 2013–2014, 35.3% of children with neurologic disorders were vaccinated, as were 28.5% of siblings and 25.0% of children in the general population.
From the 2006–2007 to the 2013–2014 influenza season, influenza vaccination coverage increased among commercially insured children in MarketScan databases. A higher proportion of children with neurologic disorders had evidence of vaccination compared with their siblings or the general pediatric sample. However, even in the season with the highest vaccination coverage, 2013–2014, less than half of children with neurologic disorders had evidence of influenza vaccination, including only approximately one-third of those 10–17 years of age. The majority of siblings of children with neurologic disorders had no evidence of vaccination, which highlights an opportunity to expand protection for children with neurologic disorders.4
Older children were vaccinated less frequently than younger children, a finding consistent with other studies.6 A previous study of children with neurologic disorders demonstrated that while estimated hospitalization rates for respiratory infections, including influenza, are highest among children less than 5 years of age, the hospitalization rate increased 14-fold in children with neurologic disorders relative to the general pediatric population, the highest relative rate of any age group.3 Older children with neurologic disorders remain vulnerable to serious consequences from respiratory infections, yet most do not receive annual influenza vaccinations; increasing vaccination coverage in this group is critical.
We found low vaccination rates for siblings of children with neurologic disorders. Beginning in 2008, 2 years after the start of this study, routine annual influenza vaccination was recommended for all persons 6 months of age and older who do not have contraindications,5 including family members and caregivers of high-risk children, both for their own protection and for additional protection for the children with whom they have close contact.4 However, we found that while siblings of children with neurologic disorders had higher influenza vaccination rates than the general pediatric population, only 28.5% of siblings were vaccinated in the most recent year for which data were available.
Other studies that use parent self-report to determine vaccination status have higher estimates for influenza vaccination coverage. For example, data from the National Immunization Surveys estimated that in 2013–2014, influenza vaccination coverage was 58.9% among children 6 months to 17 years of age compared with an estimated 34.6% in that year among the general pediatric population included in our study.6 In another survey enrolling 1005 parents of children with neurologic disorders, 50% reported that their children had received or were scheduled to receive an influenza vaccination during the 2011–2012 season,7 which was higher than our study 36.7% estimated for that season. Both these surveys used parental report of vaccination status, which likely overestimates coverage. Overestimation of coverage when relying on parental report may be even higher among children with high-risk conditions.8 MarketScan data, however, likely underestimates vaccination coverage as not all vaccinations are billed to insurance companies, and these data would likely not capture vaccinations given through schools or public health programs. This could result in the potential misclassification of vaccinated children in our study. However, most pediatric influenza vaccinations occur in doctor’s offices or other medical places, and nonbilled vaccinations likely represent a small proportion of influenza vaccinations.9 Regardless of which data are used, all estimates indicate that annual pediatric influenza vaccination coverage is far below the Healthy People 2020 goal of 70%.10
This study has limitations. In addition to potentially not capturing all influenza vaccinations, subjects were commercially insured and continuously enrolled for ≥12 months, and may not be representative of the US pediatric population. Immunization rates are lower among uninsured children or among those enrolled in government programs, such as Medicaid, compared with privately insured children. As with any large administrative dataset, diagnosis codes may be inaccurate for underlying conditions and billing code practices may be inconsistent.
Children with neurologic disorders are at greatly increased risk for hospitalization and death from influenza compared with other children. Influenza vaccination is the best tool available for protecting this vulnerable population from influenza virus infections; vaccinating family members provides additional protection.4 Influenza vaccination coverage had increased from the 2006–2007 to the 2013–2014 influenza season, but remained suboptimal for all children, including those with neurologic disorders and their siblings, especially among older children. Public health messages are needed to raise awareness of the importance of influenza vaccination in children with neurologic disorders and their close contacts, particularly aiming at parents and advocacy groups, as well as healthcare providers that care for these children. These messages should emphasize that while all persons >6 months of age should receive annual influenza vaccines, it is especially critical in vulnerable children, particularly those with neurologic disorders, as well as their families and their close contacts.
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3. Havers F, Fry AM, Chen J, et al. Hospitalizations attributable to respiratory infections among children with neurologic disorders
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8. Brown C, Clayton-Boswell H, Chaves SS, et al.; New Vaccine Surveillance Network (NVSN). Validity of parental report of influenza vaccination in young children seeking medical care. Vaccine. 2011;29:94889492.
9. Santibanez TA, Vogt TM, Zhai Y, et al. Place of influenza vaccination among children–United States, 2010-11 through 2013-14 influenza seasons. Vaccine. 2016;34:12961303.
10. Office of Disease Prevention and Health Promotion. Healthy People 2020, IID-12.11. Available at: https://www.healthypeople.gov/2020/topics-objectives/topic/immunization-and-infectious-diseases/objectives
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