The annual attack rate for influenza in children is high, the highest of any age group. It is estimated that 10% to 40% of children are infected with influenza each winter, a figure similar to the attack rate reported for children during the 2009 H1N1 pandemic.1–4
Children with underlying medical conditions bear a disproportionate burden of influenza-related morbidity and mortality.5–7 Two studies in this issue of Pediatrics add to the compelling body of evidence that children with neurologic conditions are at particularly high risk of complications resulting from influenza infection. In the first, Tran and colleagues report that children with underlying neurologic conditions in Canada had an increased risk of ICU admission after either seasonal or pandemic influenza A infection.8 In the second, Blanton et al report that neurologic disorders were identified in nearly half of all pediatric deaths associated with 2009 H1N1 pandemic influenza in the United States.9
An equally important observation from these studies, however, is the significant morbidity associated with influenza infection among children without known risk factors. Half of all hospitalizations from seasonal influenza A during 2004–2009 and almost a third of all deaths during the 2009–2010 pandemic occurred in children with no underlying medical conditions.8,9 Recent surveillance data from the United States indicate this trend continued through the 2010–2011 influenza season when 49% of pediatric deaths and 52% of pediatric hospitalizations occurred in children without a high-risk medical condition, as defined by the Advisory Committee on Immunization Practices.10,11 So while it is clear that children with certain underlying conditions are at higher risk of complications, a substantial proportion of the morbidity and mortality associated with seasonal influenza each year occurs in healthy children.10
The considerable burden of influenza disease in previously healthy children is a consequence of the high attack rate in this cohort and the fact that very young children are hospitalized from influenza illness at rates similar to other groups considered at high risk for influenza-related complications, ie adults with underlying medical conditions and those aged ≥65 years.5 It has been estimated that each year nearly one in every 1000 children under 5 years of age will be hospitalized with seasonal influenza, and that for every child admitted to a hospital another 50 are seen as outpatients.12 In recognition of this, in 2004 the Advisory Committee on Immunization Practices recommended that all children aged 6 to 23 months be vaccinated against seasonal influenza; this recommendation was subsequently expanded to include children aged 24 to 59 months in 2006, and, in 2008, ultimately extended to all persons ≥6 months to 18 years of age.13
The low rate of seasonal influenza vaccination among US children reported in the Blanton study is disappointing.9 Only 23% of children with a neurologic disorder and 12% of children with no high-risk condition who died during the 2009–2010 pandemic had received contemporaneous seasonal influenza vaccine.9 Although it is not possible to generalize vaccination rates from children who suffered an influenza-related adverse outcome to the broader population, the seasonal influenza vaccination rates reported here are not dissimilar to the US national coverage estimate (24%) for children aged 6 months to 17 years during the period just before the pandemic in 2009.14
It is fair to say that influenza vaccine uptake among both at-risk and healthy children has been slow to build but that rates increased appreciably in response to heightened concern surrounding the 2009 H1N1 pandemic.15 With memories of the pandemic still fresh in the public’s mind, the vaccination rate among US children aged 6 months to 17 years rose to 51% in 2010–2011.16 Although the increase over prepandemic vaccination levels is to be lauded, it must be acknowledged that influenza coverage for this age group is still well below the Healthy People 2020 target of 80%.16
Continual improvements in childhood influenza vaccination rates will require that providers remain convinced of the benefit of vaccination for their patients. It is therefore noteworthy that 2 recent comprehensive reviews of the efficacy of influenza vaccines have highlighted the paucity of data from randomized controlled clinical trials that support the use of inactivated influenza vaccine in children.17,18 Although both reviews found the evidence of benefit for live attenuated influenza vaccine in children to be more robust, it is currently not recommended for use among the cohort of children who arguably need protection from influenza infection the most: children <2 years of age and children with neurologic disorders or other chronic medical conditions.19,20
In their review, Jefferson and colleagues make the point that if influenza immunization of children is to be recommended as national policy, large-scale studies that directly compare vaccine types are urgently needed.17 Randomized placebo-controlled trials that assess laboratory-proven influenza infections would provide the most persuasive evidence of vaccine efficacy, but such trials cannot be conducted ethically among groups already recommended for annual influenza vaccination.21 In their absence, observational studies using different methods and measuring different outcomes have been conducted, producing mixed results.22,23 Adequately powered, multicenter observational studies that span multiple influenza seasons and use standardized criteria for laboratory and clinical endpoints could help address gaps and disparities in the existing data. Comprehensive data-linkage systems analogous to those currently used to ensure the ongoing safety of licensed childhood vaccinations may provide an appropriate model.24
Immunization remains our most promising strategy for preventing the “annual pandemic” of influenza among children. Given the high rates of influenza-related morbidity among the pediatric population, additional studies that firmly establish the impact of current vaccine recommendations should be a priority.
- Accepted April 27, 2012.
- Address correspondence to Paul V. Effler, MD, MPH, Communicable Disease Control Directorate, Department of Health, 227 Stubbs Terrace Road, Shenton Park, Australia. E-mail:
Opinions expressed in these commentaries are those of the author and not necessarily those of the American Academy of Pediatrics or its Committees.
FINANCIAL DISCLOSURE: The author has indicated they have no financial relationships relevant to this article to disclose.
FUNDING: No external funding.
- ↵American Academy of Pediatrics. Report of the Committee on Infectious Diseases. Redbook. Elk Grove Village, IL: American Academy of Pediatrics; 2009:400–412
- Broberg E,
- Nicoll A,
- Amato-Gauci A
- Fiore AE,
- Uyeki TM,
- Broder K,
- et al
- Tran D,
- Vaudry W,
- Moore D,
- et al
- Blanton L,
- Peacock G,
- Cox C,
- Jhung M,
- Finelli L,
- Moore C.
- ↵Committee on Infectious Diseases. Recommendations for prevention and control of influenza in children, 2011–2012. Pediatrics 2011;128(4):813–825
- ↵Influenza-associated pediatric deaths—United States, September 2010–August 2011. MMWR Morb Mortal Wkly Rep 2011;60(36);1233–1238.
- Neuzil KM,
- Fiore AE,
- Schieber RA
- ↵Influenza vaccination coverage among children and adults—United States, 2008–09 influenza season. MMWR Morb Mortal Wkly Rep 2009;58(39);1091–1095.
- ↵Seasonal influenza vaccination coverage among children aged 6 months–18 years—eight immunization information system sentinel sites, United States, 2009–10 influenza season. MMWR Morb Mortal Wkly Rep 2010;59(39);1266–1269.
- ↵Final state-level influenza vaccination coverage estimates for the 2010–11 season—United States, National Immunization Survey and Behavioral Risk Factor Surveillance System, August 2010 through May 2011. Available at: www.cdc.gov/flu/professionals/vaccination/coverage_1011estimates.htm. Accessed April 24, 2012.
- Jefferson T,
- Rivetti A,
- Harnden A,
- Di Pietrantonj C,
- Demicheli V
- ↵Centers for Disease Control and Prevention. Vaccine information statements live intranasal influenza vaccine. 2011–2012. Available at: www.cdc.gov/flu/pdf/protect/vis-flulive.pdf. Accessed April 24, 2012
- ↵MedImmune. LLC. FluMist influenza vaccine live, intranasal spray, 2011–2012 formula. Highlights of prescribing information. May 2011. Available at: www.medimmune.com/pdf/products/flumist_pi.pdf. Accessed April 24, 2012
- ↵Errata. MMWR Morb Mortal Wkly Rep 2010;59(RR-8):1147. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5935a6.htm. Accessed April 24, 2012
- ↵Centers for Disease Control and Prevention. Vaccine Safety Datalink Project. Available at: www.cdc.gov/vaccinesafety/Activities/VSD.html. Accessed April 24, 2012
- Copyright © 2012 by the American Academy of Pediatrics