Aug 29, 2012 (CIDRAP News) – Among kids who died during the 2009 H1N1 pandemic, the disease was most lethal for those who had neurologic conditions such as cerebral palsy and muscular dystrophy, researchers from the US Centers for Disease Control and Prevention (CDC) reported today.
The findings are a rallying call to vaccinate youngsters with underlying risk factors, according to the research team, the CDC, and children's health advocacy groups. The study appeared in an early online edition of Pediatrics.
The same journal today also carried a report from Canadian researchers that highlighted similar risks for children with neurologic conditions, and found that kids hospitalized for 2009 H1N1 were more likely to have gastrointestinal (GI) and other symptoms but not a higher death rate than those hospitalized with seasonal flu.
In the study on pediatric deaths from the 2009 H1N1 virus, the research team looked at 336 death reports that had information on underlying conditions. Pediatric flu death rates from the pandemic virus were five times higher than the median number of kids' fatalities during the previous five flu seasons.
Though health officials have known that children with neurologic disorders are at high risk for flu complications, until now it wasn't clear what the death profile was for this group among 2009 H1N1 pandemic deaths.
Of 227 children who died and had one or more underlying medical conditions, 146 (64%) had a neurologic disorder such as cerebral palsy, intellectual disability, or epilepsy, the group found.
Of those with known vaccination status, only 21 (23%) had been vaccinated against seasonal flu and 2 (3%) were fully vaccinated against 2009 H1N1 flu. The pandemic vaccine wasn't available until October 2009, when the second wave of infections was in full swing.
When researchers looked at complications in children with neurologic conditions who died from pandemic flu, the most common ones were flu-related pneumonia and acute respiratory distress syndrome (ARDS). Three-quarters of children also had an additional underlying condition that increased the risk of flu complications, such as pulmonary disorder, metabolic disorder, heart disease, or a chromosomal abnormality.
When compared with fatalities not linked to underlying risk conditions, the group with neurologic disorders was older, had longer illness duration, and was more likely to die after hospital admission, according to the study.
Lyn Finelli, DrPH, a study coauthor and chief of the CDC's surveillance and outbreak response team, said in a statement on the study from the CDC today that the high percentage of deaths from 2009 H1N1 in kids with neurologic disorders is a somber reminder of how vulnerable this group is to flu complications.
Another study coauthor, Georgina Peacock, MD, MPH, from the CDC's National Center on Birth Defects and Developmental Disabilities, said in the statement, "Flu is particularly dangerous for people who may have trouble with muscle function, lung function, or difficulty coughing, swallowing, or clearing fluids from their airways."
The CDC said it is teaming up with the American Academy of Pediatrics and advocacy groups such as Family Voices and Families Fighting Flu to raise awareness about the important of flu prevention in kids with risk factors for flu complications. The organizations will coordinate communications aimed at parents, caregivers, and medical professionals.
In 2010 the CDC launched a universal flu vaccination recommendation, urging everyone age 6 months and older to get vaccinated against seasonal flu.
In the other Pediatrics study, Canadian researchers explored whether there were differences in hospitalization patterns in the general pediatric population between the 2009 H1N1 pandemic and the five previous seasonal flu years. Their study included data from 12 Canadian pediatric hospitals that participate in a national surveillance program.
The researchers pointed out that previous studies comparing hospitalized kids infected with the two types of flu were limited to single-center populations.
The team identified 1,265 2009 H1N1 pediatric hospitalizations, of which 914 were in the second wave. They compared those patients with 1,319 seasonal influenza A cases from the 2006-07 season through the 2008-09 season.
Kids hospitalized with 2009 H1N1 infections were more likely than their seasonal-flu counterparts to present with cough, headache, and GI symptoms, be diagnosed with pneumonia, experience longer hospital stays, be older, be from a non-European ethnic group, and have asthma. However, the patients weren't at increased risk of intensive care unit (ICU) admission or death, according to the study.
Though it's not clear why patients hospitalized for 2009 H1N1 flu were more likely to have GI symptoms, the researchers said the observation may have implications for preventing the spread of the virus.
The group wrote that the increased risk of pneumonia in youngsters hospitalized with 2009 H1N1 are consistent with other findings, but they said they didn't expect to see a decreased likelihood of upper respiratory diseases such as croup.
Findings confirmed asthma as a significant risk factor in children with 2009 H1N1 infections, and the investigators also found that kids with underlying neurologic conditions—for both seasonal and pandemic flu—were at increased risk of pneumonia and ICU admission.
"Taken together, the observations from our study are consistent with animal and human data, suggesting that pH1N1 differs from seasonal influenza A viruses in its virulence and mechanisms by which it causes severe disease, potentially resulting in certain risk groups being disproportionately affected," the researchers wrote.
In an editorial in the same issue of Pediatrics that commented on both studies, Paul Effler, MD, MPH, with the Communicable Disease Control Directorate Department of Health in Shenton Park, Australia, wrote that the two studies bolster a compelling body of evidence that kids with neurologic conditions are at high risk for flu complications.
"An equally important observation from these studies, however, is the significant morbidity associated with influenza infections among children without known risk factors," he wrote.
Effler added that the low rate of seasonal flu vaccination seen in the first study is disappointing, and though health officials have made some headway at boosting levels to about 51% in the wake of the 2009 H1N1 pandemic, coverage is still well below the Healthy People 2020 target of 80%.
Vaccination efforts would benefit from health provider confidence that the flu vaccine is beneficial for kids, he wrote, pointing to recent reviews of flu vaccine efficacy that found little data from randomized controlled clinical trials that support the efficacy of the inactivated flu vaccine for kids.
Though efficacy for the live attenuated flu vaccine appears to be more robust, it is not recommended for kids who may need protection the most: those younger than 2 and those with neurologic disorders or other underlying conditions, he wrote.
Effler added that immunization is still the most promising strategy for preventing the "annual pandemic" of flu in children and that more powerful studies that include several flu seasons and use standard lab criteria and clinical end points could help address data gaps and support current vaccine recommendations.
Blanton L, Peacock G, Cox C, et al. Neurologic disorders among pediatric deaths associated with the 2009 pandemic influenza. Pediatrics 2012 Sep;130(3):390-6 [Abstract]
Tran D, Vaudry W, Moore DL, et al. Comparison of children hospitalized with seasonal versus pandemic influenza A, 2004-2009. Pediatrics 2012Sep;130(3):397-406 [Abstract]
Effler PV. Every year is an influenza pandemic for children: can we stop them? Editorial. Pediatrics 2012 Sep;130(3):554-6 [Abstract]
Aug 29 CDC press release