Vaccine effectiveness against medically attended, laboratory-confirmed influenza among children aged 6 to 59 months, 2003-2004.
OBJECTIVE
Influenza is a leading cause of illness among children. Studies rarely have measured influenza vaccine effectiveness among young children, particularly when antigenic match between vaccine and circulating viruses is suboptimal. We assessed vaccine effectiveness against medically attended, laboratory-confirmed influenza for children who were aged 6 to 59 months during the 2003-2004 influenza season.


METHODS
In a case-control study that was conducted in a single pediatric practice, case patients who were aged 6 to 59 months and had laboratory-confirmed influenza were age matched 1:2 to eligible control subjects. Vaccination status was ascertained as of the date of the case patient's symptom onset. Conditional logistic regression was used to calculate vaccine effectiveness, adjusting for underlying medical conditions and health care usage.


RESULTS
We identified 290 influenza case patients who were seen for medical care from November 1, 2003, to January 31, 2004. Vaccine effectiveness among fully vaccinated children, compared with unvaccinated children, was 49%. Partially vaccinated children who were aged 6 to 23 months had no significant reduction in influenza (vaccine effectiveness: -70%), but partially vaccinated children who were aged 24 to 59 months had a significant (65%) reduction in influenza, compared with unvaccinated children.


CONCLUSIONS
Full vaccination provided measurable protection against laboratory-confirmed influenza among children who were aged 6 to 59 months during a season with suboptimal vaccine match. No vaccine effectiveness was identified with partial vaccination among children who were aged 6 to 23 months, affirming that children need to be fully vaccinated to obtain protective effects. These results strengthen the evidence of the vaccine's ability to reduce substantially the burden of disease in this age group.
Shuler
Carrie M
CM
Epidemic Intelligence Service, Atlanta, GA, USA. cmshuler@dhr.state.ga.us
Iwamoto
Martha
M
Bridges
Carolyn Buxton
CB
Marin
Mona
M
Neeman
Ruth
R
Gargiullo
Paul
P
Yoder
Terrace A
TA
Keyserling
Harry L
HL
Terebuh
Pauline D
PD
D000367:Age Factors; D016022:Case-Control Studies; D002675:Child, Preschool; D015897:Comorbidity; D003371:Cough / Q000453:epidemiology; D005260:Female; D005334:Fever / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D016015:Logistic Models; D008297:Male; D015999:Multivariate Analysis; D009975:Orthomyxoviridae / Q000276:immunology*; D016896:Treatment Outcome; D014839:Vomiting / Q000453:epidemiology
D007252:Influenza Vaccines