The effects of school closures on influenza outbreaks and pandemics: systematic review of simulation studies

Abstract

Background: School closure is a potential intervention during an influenza pandemic and has been investigated in many modelling studies.

Objectives: To systematically review the effects of school closure on influenza outbreaks as predicted by simulation studies.

Methods: We searched Medline and Embase for relevant modelling studies published by the end of October 2012, and handsearched key journals. We summarised the predicted effects of school closure on the peak and cumulative attack rates and the duration of the epidemic. We investigated how these predictions depended on the basic reproduction number, the timing and duration of closure and the assumed effects of school closures on contact patterns.

Results: School closures were usually predicted to be most effective if they caused large reductions in contact, if transmissibility was low (e.g. a basic reproduction number <2), and if attack rates were higher in children than in adults. The cumulative attack rate was expected to change less than the peak, but quantitative predictions varied (e.g. reductions in the peak were frequently 20-60% but some studies predicted >90% reductions or even increases under certain assumptions). This partly reflected differences in model assumptions, such as those regarding population contact patterns.

Conclusions: Simulation studies suggest that school closure can be a useful control measure during an influenza pandemic, particularly for reducing peak demand on health services. However, it is difficult to accurately quantify the likely benefits. Further studies of the effects of reactive school closures on contact patterns are needed to improve the accuracy of model predictions.

Figure 1. Summary of the estimated effects of school closures on peak incidence of pandemic influenza (all ages) predicted by the modelling studies.

Different symbols are used to reflect the assumed value for R₀. The findings are grouped according to whether they assumed that the community/household contacts increased, remained unchanged, the assumptions about contact were based on empirical data or were unclear. Some studies assumed that workplaces and/or other public places also closed , , . All studies that stated their assumptions regarding the effects of school closure on contact patterns assumed that contacts between school-aged children were reduced or eliminated.

Figure 2. Summary of the estimated effects of school closures on cumulative incidence of pandemic influenza (all ages) predicted by the modelling studies.

Different symbols are used to reflect the assumed value for R₀. The findings are grouped according to whether they assumed that the community/household contacts increased, remained unchanged, the assumptions about contact were based on empirical data or were unclear. Some studies assumed that workplaces and/or other public places also closed , , . All studies that stated their assumptions regarding the effects of school closure on contact patterns assumed that contacts between school-aged children were reduced or eliminated.

Figure 3. Plot of the predicted reduction in the cumulative attack rate against that in the peak incidence (all ages).

Each marker represents the results of one analysis. Different symbols are used to reflect different values for R₀.

Figure 4. Influence of the duration of school closure on the predicted effects on pandemic influenza.

Reductions in peak incidence (A and B) and cumulative attack rates (C and D) for different values of R₀ and assumed thresholds for school closure. Lines join predictions from the same model using the same sets of assumptions.