Effectiveness of the 2003-2004 influenza vaccine among children 6 months to 8 years of age, with 1 vs 2 doses

Clinical Research Unit, Kaiser Permanente Colorado, 580 Mohawk Dr, Boulder, CO 80302, USA.
PEDIATRICS (Impact Factor: 5.3). 07/2005; 116(1):153-9. DOI: 10.1542/peds.2005-0049
Source: PubMed

ABSTRACT To evaluate the effectiveness of 1 and 2 doses of the 2003-2004 influenza vaccine in preventing medically attended influenza-like illness (ILI) among children 6 to 23 months and 6 months to 8 years of age. Design and
Outpatient and emergency department visits and immunization records were used to conduct a retrospective cohort study among children 6 months to 8 years of age. ILI and pneumonia and influenza (P&I) outcomes were defined on the basis of International Classification of Diseases, Ninth Revision, codes. Influenza vaccine effectiveness (VE) was calculated as (1 - hazard rate ratio) x 100.
A total of 29726 children were included in the analyses; 17.3% were 6 to 23 months of age. By November 19, 2003, the start of peak influenza activity, 7.5% and 9.9% of children 6 months to 8 years were fully or partially vaccinated against influenza, respectively. For fully vaccinated children 6 to 23 months of age, VE against ILI and P&I was 25% and 49%, respectively. No statistically significant reduction in ILI or P&I rates was observed for partially vaccinated children 6 to 23 months of age (-3% and 22%, respectively). For fully vaccinated children 6 months to 8 years of age, VE against ILI and P&I was 23% and 51%, respectively. For partial vaccination, VE was significant only for P&I (23%).
Despite a suboptimal match between the influenza vaccine and predominant circulating strains, influenza vaccination provided substantial protection for fully vaccinated children and possibly some protection for partially vaccinated children <9 years of age. These findings support vaccinating targeted children even when the vaccine match is suboptimal, and they highlight the need to vaccinate previously unvaccinated children with 2 doses for optimal protection.

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    • "Cost of subsidy for children in Isahaya City was the same from infants until the graduation of elementary school. In a previous study conducted among children, the vaccination coverage rate was 41.6% for children aged from 6-23 months and 26.1% for those aged 2-8 years (Ritzwoller et al. 2005). One of the reasons for the lower vaccination rate in older children was that their parents tended to visit the pediatric facilities less frequently and get less information about influenza vaccination (Ando 2012). "
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    The Tohoku Journal of Experimental Medicine 02/2014; 232(2):97-104. DOI:10.1620/tjem.232.97 · 1.28 Impact Factor
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    • "Due to the poorer immune response in the elderly, this may be more important in this group than in healthy adults (de Jong et al 2000). In healthy subjects, however, the vaccine is effective (49%–53%) in preventing illness also in years with a sub-optimal match between the vaccine and circulating infl uenza strains (Pyhälä et al 2001; Ritzwoller et al 2005). The level of circulating infl uenza in the community also complicates the calculation of the effectiveness of the vaccine. "
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    MMWR. Recommendations and reports: Morbidity and mortality weekly report. Recommendations and reports / Centers for Disease Control 08/2010; 59(RR-8).
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