Establishing the baseline burden of influenza in preparation for the evaluation of a countywide school-based influenza vaccination campaign.

Grijalva CG, Zhu Y, Simonsen L, Griffin MR
Vaccine. 2010 29 (1): 123-9

PMID: 21050905 · PMCID: PMC4818949 · DOI:10.1016/j.vaccine.2010.08.072

BACKGROUND - School-based influenza vaccination campaigns could mitigate the effects of influenza epidemics. A large countywide school-based vaccination campaign was launched in Knox County, Tennessee, in 2005. Assessment of campaign effects requires identification of appropriate control populations. We hypothesized that contiguous counties would share similar pre-campaign patterns of influenza activity.

METHODS - We compared the burden of influenza emergency department (ED) visits and hospitalizations between Knox County (Knox) and eight counties surrounding Knox (Knox-surrounding) during five consecutive pre-campaign influenza seasons (2000-01 through 2004-05). Laboratory-defined influenza seasons were used to measure the weekly incidence of medically attended acute respiratory illnesses (MAARI) attributable to influenza in school-aged children 5-17 years old (campaign target) as well as in other age groups. Seasonal rates of MAARI attributable to influenza for Knox and Knox-surrounding counties were compared using rate ratios.

RESULTS - During five consecutive influenza seasons, MAARI attributable to influenza showed synchronous temporal patterns in school-aged children from Knox and Knox-surrounding counties. The average seasonal rates of ED visits attributable to influenza were 12.37 (95% CI: 10.32-14.42) and 13.14 (95% CI: 11.23-15.05) per 1000, respectively. The respective average seasonal influenza hospitalization rates for Knox and Knox-surrounding were 0.38 (95% CI: 0-0.79) and 0.46 (95% CI: 0.07-0.85) per 1000 children. Rate ratio analyses indicated no significant differences in the incidence of MAARI attributable to influenza between school-aged children from Knox and Knox-surrounding counties. Estimates for other age groups showed similar patterns.

CONCLUSION - Before the Knox school-based influenza vaccination campaign, influenza resulted in an average of about 12 ED visits and 0.4 hospitalizations per 1000 school-aged children annually in Knox County. Since similar morbidity was observed in surrounding counties, they could serve as a control population for the assessment of the campaign effects.

Copyright © 2010. Published by Elsevier Ltd.

MeSH Terms (22)

Adolescent Adult Aged Aged, 80 and over Ambulatory Care Child Child, Preschool Emergency Medical Services Female Hospitalization Humans Incidence Influenza, Human Influenza Vaccines Male Middle Aged Orthomyxoviridae Schools Students Tennessee Vaccination Young Adult

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