School-located influenza vaccination decreases laboratory-confirmed influenza and improves school attendance

Abstract

Background: School-located influenza vaccination (SLV) programs can efficiently immunize large numbers of school-aged children. We evaluated the impact of SLV on laboratory-confirmed influenza and absenteeism.

Methods: Active surveillance for influenza-like illness (ILI) was conducted on 4455 children in 4 SLV intervention and 4 control elementary schools (grades K-6) matched for sociodemographic characteristics during the 2010-2011 influenza season in Los Angeles County, California. Combined nose/throat swabs were collected from febrile children with ILI at presentation to the school nurse or during absenteeism.

Results: In SLV schools, 26.9%-46.6% of enrolled students received at least 1 dose of either inactivated or live attenuated influenza vaccine compared with 0.8%-4.3% in control schools. Polymerase chain reaction for respiratory viruses (PCR) was performed on 1021 specimens obtained from 898 children. Specimens were positive for influenza in 217 (21.3%), including 2009 H1N1 (30.9%), H3 (9.2%), and B (59.9%). Children attending SLV schools, regardless of vaccination status, were 30.8% (95% confidence interval, 10.1%-46.8%) less likely to acquire influenza compared with children at control schools. Unvaccinated children were indirectly protected in the school with nearly 50% vaccination coverage compared with control schools (influenza rate, 27.1 vs 60.0 per 1000 children; P = .023). Unvaccinated children missed more school days than vaccinated children (4.3 vs 2.8 days per 100 school days; P < .001).

Conclusions: Vaccination of at least a quarter of the school population resulted in decreased influenza rates and improved school attendance. Herd immunity for unvaccinated children may occur in schools with vaccination coverage approaching 50%.

Keywords: herd immunity; influenza; influenza vaccine; school-located influenza vaccination.

Figure 1.

Influenza vaccination coverage in intervention and control schools by school-located vaccination (SLV) and community physicians, as documented in the Los Angeles-Orange County California immunization registry, 2010–2011.

Figure 2.

A, Respiratory viruses identified by reverse transcription-polymerase chain reaction (RT-PCR) from 343 (33.6%) children with influenza-like illness (ILI) from all study schools, Los Angeles County, 2010–2011. Significantly more influenza viruses were detected compared with other viruses. RT-PCR did not identify a respiratory virus in 678 (66.3%) children with ILI. B, Incidence rates of PCR-confirmed influenza and noninfluenza respiratory viruses in control and intervention schools. Higher rates of influenza were observed in control schools without school-located influenza vaccination (SLV) programs (58.0 vs 40.1 per 1000 children; P = .006), while rates of noninfluenza respiratory viruses remained similar in control and SLV intervention schools (30.8 vs 24.0 per 1000 children; P = .163).

Figure 3.

Polymerase chain reaction (PCR)–confirmed influenza rates in control and school-located influenza vaccination intervention schools by vaccination coverage during influenza-like illness surveillance period in all enrolled children, regardless of vaccination status (A) and in all unvaccinated children (B), Los Angeles County, 2010–2011.

Figure 4.

Influenza-like illness during the surveillance period in school-located influenza vaccination intervention and control schools by influenza vaccination coverage rates, Los Angeles County, 2010–2011.