Effectiveness of inactivated influenza vaccine in children less than 5 years of age over multiple influenza seasons: a case-control study.
Joshi AY1, Iyer VN, St Sauver JL, Jacobson RM, Boyce TG.
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Abstract
The effectiveness of influenza vaccine over multiple influenza seasons in children less than 5 years of age has not been well studied. This is especially important to assess because of the recent recommendation for routine influenzavaccination in childhood. We conducted a matched case-control study to assess the vaccine effectiveness of Trivalent Inactivated Influenza Vaccine (TIV) against laboratory-confirmed, medically attended influenza among children 6-59 months of age at the start of each influenza season from 1999-2000 through 2006-2007 in Olmsted County, MN, USA. The children vaccinated against influenza accordingly to the 2007 ACIP guidelines had a lower risk of laboratory-confirmed medically attended influenza illness (Odds Ratio: 0.14, 95% Confidence Interval: 0.03-0.71) than the unvaccinated children. TIV provided strong protection against laboratory-confirmed medically attended influenza in children 6-59 months old in the fully vaccinated group. This trend continued in the partially vaccinated group (Odds Ratio: 0.27, 95% Confidence Interval: 0.07-0.97) but the protection provided maybe suboptimal.
Effectiveness of trivalent inactivated influenza vaccine in influenza-related hospitalization in children: a case-control study.
Joshi AY1, Iyer VN, Hartz MF, Patel AM, Li JT.
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Abstract
Influenza is known to be associated with asthma exacerbation but the effectiveness of the trivalent inactivated flu vaccine (TIV) in children, especially children with asthma, in preventing hospitalization is unknown. We assessed the effectiveness of the TIV in all children and especially children with asthma to prevent hospitalization with influenza. We conducted a nested case control study of all pediatric subjects (6 months to 18 years old) who were evaluated at the Mayo Clinic, Rochester, MN, who had laboratory-confirmed influenza during each flu season from 1999 to 2006 to evaluate the efficacy of TIV in preventing hospitalization. A case-control analysis was performed with the cases and the controls being the subjects who did and did not required hospitalization with the influenza illness, respectively. There were 261 subjects with laboratory-confirmed influenza from 1996 to 2006. There was an overall trend toward higher rates of hospitalization in subjects who got the TIV when compared with the ones who did not get the TIV (odds ratio [OR], 3.67; CI, 1.6, 8.4). Using the Cochran-Mantel-Haenszel test for asthma status stratification, there was a significant association between hospitalization in asthmatic subjects and TIV (p = 0.001). TIV did not provide any protection against hospitalization in pediatric subjects, especially children with asthma. On the contrary, we found a threefold increased risk of hospitalization in subjects who did get the TIV vaccine. This may be a reflection not only of vaccine effectiveness but also the population of children who are more likely to get the vaccine.