The Advisory Committee on Immunization Practices recommends universal flu vaccination for children aged 6 to 23 months, but recommends shots for older children only if they have high-risk medical conditions. But an analysis at Children's Hospital Boston suggests that otherwise healthy 3- and 4-year-olds drive flu epidemics and should also be considered for vaccination.
The researchers leveraged a real-time computerized biosurveillance system linking five diverse ambulatory and emergency care settings in Greater Boston. Examining medical visits from 2000 to 2004, they found that children aged 3 to 4 clearly led influenza epidemics, presenting with flu-like respiratory illness as early as late September. Children aged 2 and younger began presenting a week or two later, while older children first presented in October and adults only in November.
Moreover, flu-like illness in children under age 5 was the most predictive of pneumonia and influenza mortality in the general population, as reported to the Centers for Disease Control and Prevention. Hospital visits by children aged 2 and younger provided the best prediction of mortality, but those of 3- and 4-year-olds followed close behind, suggesting that preschoolers, not just infants and toddlers, are important flu spreaders.
"This makes sense, since preschools and daycare centers are hotbeds of infection," says John Brownstein, PhD, first author of the paper and a researcher in Children's programs in Informatics and Emergency Medicine.
Senior investigator Kenneth Mandl, MD, MPH, an attending physician in Children's Department of Emergency Medicine and research director of Children's Biopreparedness Center, believes the findings support a change in immunization practice. "General influenza immunization policies target high-risk individuals," he says. "But in a flu pandemic, you might want to reallocate and vaccinate the people who are spreading flu to everyone else."
The study, published in the October 1 American Journal of Epidemiology, drew on two real-time population health monitoring systems: the Automated Epidemiological Geotemporal Integrated Surveillance system, or AEGIS, developed by Children's Department of Emergency Medicine, and the National Bioterrorism Syndromic Surveillance Demonstration Project.
"Millions of federal dollars are invested in real-time surveillance to detect bioterrorism," Mandl says. "But these systems also have a peacetime use, allowing us to look very quickly at the transmission dynamics of diseases like influenza."