Effectiveness of the 2003-2005
Influenza Vaccine among Children 6 months to 8 years, with 1 vs 2
doses
Ritzwoller DP,
Bridges CB,
Shetterly S,
Yamasaki K,
Kolczak M,
France EK.
Clinical Research Unit, Kaiser Permanente Colorado, 580 Mohawk Dr, Boulder,
CO 80302, USA. debra.ritzwoller@kp.org
OBJECTIVE: 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
METHODS: 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. RESULTS: 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%). CONCLUSIONS:
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.
Pediatrics. 2005 Jul;116(1):153-9.
