Methods: Active surveillance was conducted on 4465 children in 4 control and 4 SLIV intervention elementary schools (grades K-6) matched for sociodemographic characteristics in an urban community during the 2010-11 influenza season. Polymerase chain reaction for respiratory viruses was performed on nose and throat swabs collected from febrile children with influenza-like illness at presentation to the school nurse or during absenteeism.
Results: In the SLIV intervention schools, 27.8 to 47.3% of the students received at least one dose of influenza vaccine. PCR results are available to date on 913 specimens obtained from 1030 children during the 15 week surveillence period. Specimens were positive for influenza in 208 (22.8%) including 2009 H1N1 (30.8%), H3 (8.7%) and B (60.6%); 101 (11.1%) were positive for other respiratory viruses. Influenza rates were higher in control schools compared to intervention (5.5 vs. 3.9 per 100 children, p=0.011). Unvaccinated children attending any school were 2.9 times more likely to acquire influenza compared to vaccinated children (5.2 vs. 1.6 per 100 children, p<0.001). Protection for unvaccinated children was only seen in the one school that achieved 47.3% vaccination rate (OR 2.1, p=0.039). Absenteeism rates were higher in control compared to SLIV intervention schools (4.2 vs. 3.9 per 100 school days, p =0.023) during influenza season. Children with influenza missed a median of 2 days (range: 1-7 days) of school per illness episode compared to 1 day (range: 1-10 days) missed for children with other respiratory viruses (p<0.001).
Conclusion: Vaccination of at least a quarter of the school population results in decrease influenza rates and improves school attendance. Herd immunity for unvaccinated children may occur in schools with vaccination rates approaching 50 percent.
H. Wang, None
C. Ha, None
H. Rivas, None
M. Smit, None
G. Aldrovandi, None
L. Mascola, Merck: Speaker's Bureau, Speaker honorarium
MedImmune: Speaker's Bureau, Speaker honorarium