Current immunization policies recommend universal flu vaccination forchildren aged 6-23 months, but shots are advised for older childrenonly if they have high-risk medical conditions. New data compiled byresearchers at Children's Hospital Boston and Harvard Medical School,reported in October 1 issue of the American Journal of Epidemiology,suggest that otherwise healthy 3- and 4-year-olds drive flu epidemics,a pattern that may warrant consideration when formulating immunizationpolicy.
The researchers leveraged a real-time computerized biosurveillancesystem linking five diverse health-care settings in Greater Boston, andexamined medical visits from 2000 to 2004. Children aged 3 to 4 clearlyled influenza epidemics, presenting with flu-like respiratory illnessas early as late September. Children aged 0-2 began arriving a week ortwo later, while older children first arrived in October and adultsbegan arriving only in November.
Moreover, flu-like illness in children under age 5, comparedwith all other age groups, was the most predictive of pneumonia andinfluenza deaths in the general population as determined from a Centersfor Disease Control and Prevention database. Visits by children aged0-2 provided the best prediction of mortality, but those of 3- and4-year-olds followed close behind, suggesting that preschoolers, notjust infants and toddlers, are important spreaders of flu to vulnerablegroups.
"The data make sense because preschools and daycares, withtheir close quarters, are hotbeds of infection," says Dr. JohnBrownstein, the paper's lead author and a faculty member of theChildren's Hospital Informatics Program at the Harvard-MIT HealthSciences and Technology program. "The data suggest that when kids aresneezing, the elderly begin to die. Three- and 4-year-olds aresentinels that allow us to focus our surveillance systems."
Influenza kills tens of thousands of Americans each year.Previous studies have shown decreases in household flu transmission andin adult flu mortality when children are immunized. Additional studieshave also suggested that preschoolers drive flu epidemics, but they arebased on simulations.
"Our study was not a simulation," says senior investigator Dr.Kenneth Mandl, an attending physician in Children's Department ofEmergency Medicine and an informatics program faculty member. "This wasreal life."
Brownstein and Mandl believes that the surveillance datasupport a different approach to immunization, one based not on who's atrisk for influenza, but on who's spreading the disease.
"General influenza immunization policies target high-riskindividuals -- kids under 24 months, the elderly, and people withunderlying disease," Mandl says. "But if avian flu is coming in and youwant to stop it from spreading, you might want to vaccinate the peoplewho are transmitting it to everyone else. In a pandemic, where peopleare getting sick and dying, you might want to reallocate who gets thevaccine."
The study drew its data from two real-time population healthmonitoring systems: the Automated Epidemiological GeotemporalIntegrated Surveillance system, or AEGIS, developed by Children'semergency department, and the National Bioterrorism SyndromicSurveillance Demonstration Project. The health care settings analyzedwere pediatric, adult, general and community emergency departments anda large HMO network.
"Millions of federal dollars are invested in real-timesurveillance to detect bioterrorism," Mandl points out. "But thesesystems have a dual use, allowing us to look very quickly at thetransmission dynamics of diseases like influenza during peacetime."
To view the article online, visit http://aje.oxfordjournals.org/cgi/content/abstract/kwi257?ijkey=suOWPGGM3oyD7Sl&keytype=ref
Founded in 1869 as a 20-bed hospital for children, Children'sHospital Boston today is the nation's leading pediatric medical center,the largest provider of health care to Massachusetts children, and theprimary pediatric teaching hospital of Harvard Medical School. Inaddition to 347 pediatric and adolescent inpatient beds andcomprehensive outpatient programs, Children's houses the world'slargest research enterprise based at a pediatric medical center, whereits discoveries benefit both children and adults. More than 500scientists, including eight members of the National Academy ofSciences, nine members of the Institute of Medicine and 10 members ofthe Howard Hughes Medical Institute comprise Children's researchcommunity. For more information about the hospital visit: http://www.childrenshospital.org.
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