School closures and influenza: systematic review of epidemiological studies

Abstract

Objective: To review the effects of school closures on pandemic and seasonal influenza outbreaks.

Design: Systematic review.

Data sources: MEDLINE and EMBASE, reference lists of identified articles, hand searches of key journals and additional papers from the authors' collections.

Study selection: Studies were included if they reported on a seasonal or pandemic influenza outbreak coinciding with a planned or unplanned school closure.

Results: Of 2579 papers identified through MEDLINE and EMBASE, 65 were eligible for inclusion in the review along with 14 identified from other sources. Influenza incidence frequently declined after school closure. The effect was sometimes reversed when schools reopened, supporting a causal role for school closure in reducing incidence. Any benefits associated with school closure appeared to be greatest among school-aged children. However, as schools often closed late in the outbreak or other interventions were used concurrently, it was sometimes unclear how much school closure contributed to the reductions in incidence.

Conclusions: School closures appear to have the potential to reduce influenza transmission, but the heterogeneity in the data available means that the optimum strategy (eg, the ideal length and timing of closure) remains unclear.

Figure 1

Identification of epidemiological studies of the effects of school closure on influenza outbreaks.

Figure 2

Peak cumulative attack rates recorded in the identified studies. Case definitions varied between studies (see online supplementary appendix); only studies which included a denominator are shown. Studies which reported peak prevalence of absenteeism are denoted by an asterisk. See online supplementary appendix for full details of datasets. All pandemic data are from 2009 except for Kelleys Island. BC, British Columbia; CT, Connecticut; IL, Illinois; KI, Kelleys Island; NC, North Carolina.

Figure 3

Normalised peak attack rates (estimated as peak attack rate/median attack rate) recorded in the identified studies; one study with an estimate normalised peak of 128 is excluded for clarity. Case definitions varied between studies (see online supplementary appendix). Studies which reported peak prevalence of absenteeism are denoted by an asterisk. HK, Hong Kong; IL, Illinois; KI, Kelleys Island; NC, North Carolina; SARI, severe acute respiratory infection.