Review
Evidence compendium and advice on social distancing and other related measures for response to an influenza pandemic

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Summary

The role of social distancing measures in mitigating pandemic influenza is not precisely understood. To this end, we have conducted a systematised review, particularly in light of the 2009 pandemic influenza, to better inform the role of social distancing measures against pandemic influenza.

Articles were identified from relevant databases and the data were synthesised to provide evidence on the role of school or work place-based interventions, case-based distancing (self-isolation, quarantine), and restriction of mobility and mass gatherings.

School closure, whether proactive or reactive, appears to be moderately effective and acceptable in reducing the transmission of influenza and in delaying the peak of an epidemic but is associated with very high secondary costs. Voluntary home isolation and quarantine are also effective and acceptable measures but there is an increased risk of intra-household transmission from index cases to contacts. Work place-related interventions like work closure and home working are also modestly effective and are acceptable, but likely to be economically disruptive. Internal mobility restriction is effective only if prohibitively high (50% of travel) restrictions are applied and mass gatherings occurring within 10 days before the epidemic peak are likely to increase the risk of transmission of influenza.

Introduction

In an average season between 0.3 and 9.8% children present with influenza for medical attention; this incidence is greater in children under 5 years of age [1]. Globally, an estimated 90 million cases of influenza occur each year in children aged under 5, of which an estimated 20 million are associated with acute lower respiratory tract infection [2]. For pandemic strains the burden can be greater, with elevated hospital and emergency departments admission rates throughout the population [1], elevated death rates and wider socioeconomic impacts [3]. Pandemic plans have been developed by organisations such as the WHO, individual countries and local groups such as businesses, in an attempt to mitigate such risks. Amongst the public health measures considered (e.g., vaccination, antiviral stock piling), those that promote reduced infectious contact in societies, or “social distancing” may complement other pandemic planning measures in decreasing the likelihood and severity of pandemic influenza transmission.

In contrast to technological interventions such as vaccination and anti-viral drugs, published evidence of the efficacy or effectiveness of individual measures for social distancing is limited. The European Centre for Disease Prevention and Control (ECDC) published a technical report on public health measures to reduce pandemic influenza impact [4] that identified gaps in our understanding of the role of social distancing measures in pandemic planning. However, the 2009 H1N1 influenza pandemic has stimulated more research in this area, including clinical and epidemiological studies, and mathematical modeling. Pandemic plans in a number of countries, including Australia are currently being revised in light of published reviews of their effectiveness and therefore, it is timely to identify and review the latest evidence regarding the potential impacts of social distancing and related measures [5]. This review assessed the impact of the following measures: proactive or reactive school closure, workplace closure, working from home, isolation of cases and/or contacts (quarantine), internal mobility restriction and cancellation of mass events.

Section snippets

Search strategy

Database searching was undertaken by an experienced medical librarian (CK) in December 2012. A copy of the full search can be obtained by contacting the authors; in short, the following databases/sources were searched - Ovid Medline (1946 to November Week 3 2012), Ovid Embase (1980 to December Week 3 2012), Cochrane Library (Database of Systematic Reviews Issue 12 of 12, December 2012, Database of Abstracts of Reviews of Effects Issue 4 of 4, October 2012, Central Register of Controlled Trials

Results

The effectiveness and limitations of each individual intervention are summarised in Table 1, Table 2, and described below.

Evidence of effectiveness

Studies suggest that school closure, whether proactive or reactive, reduces transmission of influenza and delays the epidemic peak. The majority of modeling and observational studies suggest a reduction in influenza occurrence or transmission following school closure but with wide variance (range 1-50%) [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. Other studies, in which transmission between children is assumed to be very influential, have

Evidence of effectiveness

We found only 3 empirical studies examining the impact of changes to work arrangements on influenza transmission risks, with a US study during 2009-10 finding reduced risks of self-reported ILI among individuals who could work from home (8.2% versus 12.8%, p<0.05) or stay home from work for 7-10 days (8.8% vs 12.2% p<0.05) compared with those who could not [50]. In a quasi-cluster randomised trial conducted in Japan in 2009, the workplace policy of being able to remain at home on full pay

Evidence of effectiveness

There were limited studies evaluating these measures, with moderate effectiveness found in modeling simulations. A Japanese modeling study suggested that total community infections would fall as the proportion of children or adults isolated at home increased [16], with support from other modeling studies [56], [57].

Simulations of quarantining household contacts of index cases also suggests benefit [19], [58], [59]. In a modeling study applied to Mongolia (a useful example in terms of its

Evidence of effectiveness

Modeling studies comprise most recent research in this area, although a systematic review suggests some mass gatherings are associated with increased influenza transmission, while archival studies of the 1918-19 pandemic imply that restricting mass gatherings was beneficial, particularly with early implementation [74]. A modeling paper suggested that mass gatherings shortly before the epidemic peak could increase the peak height by about 10% but at other times, the impact would be small.[75]

Overall effectiveness and quality of the evidence

A large number of published studies examining social distancing have been conducted since the 2009 pandemic of influenza. Overall, social distancing measures are found to be moderately effective.

School or workplace closures and case-based measures such as isolation and quarantine of contacts are found to be at least modestly effective, but are likely to be costly and disruptive. Mobility restrictions may not be effective unless prohibitively high restrictions are applied and are likely to be

Conclusion

Since the 2009 pandemic, more published evidence on the effectiveness of social distancing measures in mitigating pandemic influenza has appeared. Overall, social distancing measures appear modestly effective and many are likely to be acceptable in the short term, but there is a lack of strong evidence.

Future Research Directions

  • As there is a dearth of high quality studies, controlled trials should be prioritised in this field

  • The evidence compendium needs to be updated periodically to incorporate emerging evidence

  • Systematic reviews on the interaction between individual measures should be undertaken, including wider interventions like face masks, vaccines and antivirals

Educational Aims

The readers will become familiar with:

  • Critical evaluation of the impact of social distancing measures against pandemic influenza in light of the latest evidence

  • Direct and indirect costs of implementing certain social distancing measures (e.g., school and workplace closures) in mitigating pandemic influenza

  • Acceptability of social distancing measures among members of public and their expectations

Acknowledgement

This study was funded by the Australian Department of Health obtained through a tender process (RFQ No: DoHA/130/1213). Iman Ridda holds an NHMRC Early Career Fellowship (630739) and James Wood has received partial salary support from NHMRC CRE 1021963.

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