Non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza

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Executive Summary

Introduction

Influenza pandemics occur at unpredictable intervals, and cause considerable morbidity and mortality. Influenza virus is readily transmissible from person to person, mainly during close contact, and is challenging to control. In the early stage of influenza epidemics and pandemics, there may be delay in the availability of specific vaccines and limited supply of antiviral drugs. Non-pharmaceutical interventions (NPIs) are the only set of pandemic countermeasures

that are readily available at all times and in all countries. The potential impacts of NPIs on an influenza epidemic or pandemic are to delay the introduction of the pandemic virus into a population; delay the height and peak of the epidemic if the epidemic has started; reduce transmission by personal protective or environmental measures; and reduce the total number of infections and hence the total number of severe cases.

Scope and purpose

This document provides recommendations for the use of NPIs in future influenza epidemics and pandemics based on existing guidance documents and the latest scientific literature.
The specific recommendations are based on a systematic review of the evidence on the effectiveness of NPIs, including personal protective measures, environmental measures, social distancing measures and travel-related measures. The information provided here will be useful for national authorities that are developing or updating their plans for mitigating the impact of influenza epidemics and pandemics.

Target audience

This guideline is intended to support the development and updating of national plans for mitigating influenza epidemics and pandemics in community settings. The recommendations included in this guideline will also be of interest to individuals, organizations, institutions and local health authorities.

Methods

The guideline development process included the following stages:

  1. Identify a list of NPIs that have the potential to contribute to pandemic mitigation for further review and evaluation.

  2. Identify and evaluate existing systematic reviews of the NPIs listed in Step 1, and perform new systematic reviews for each NPI if recently published reviews were not available.

  3. Assess the body of evidence on the effectiveness of each of the NPIs.

  4. Determine the direction and strength of recommendations.

  5. Draft the guideline document based on evidence and planning for strategy implementation.

The guideline development process included the formation of four main groups: a World Health Organization (WHO) guideline steering group, a systematic review team from the University of Hong Kong, a guideline development group and an external review group. The primary responsibilities of these four groups are, respectively, to oversee the process
of the guideline development, to review the evidence base for each NPI, to formulate recommendations based on scientific evidence and other considerations, and to review the guidelines.

world health organization

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Available evidence

The evidence base for this guideline included systematic reviews of 18 NPIs, covering:

  • personal protective measures (e.g. hand hygiene, respiratory etiquette and face masks);

  • environmental measures (e.g. surface and object cleaning, and other environmental measures);

  • social distancing measures (e.g. contact tracing, isolation of sick individuals, quarantine of exposed individuals, school measures and closures, workplace measures and closures, and avoiding crowding); and

  • travel-related measures (e.g. travel advice, entry and exit screening, internal travel restrictions and border closure).

    The evidence base on the effectiveness of NPIs in community settings is limited, and the overall quality of evidence was very low for most interventions. There have been a number of high- quality randomized controlled trials (RCTs) demonstrating that personal protective measures such as hand hygiene and face masks have, at best, a small effect on influenza transmission, although higher compliance in a severe pandemic might improve effectiveness. However, there are few RCTs for other NPIs, and much of the evidence base is from observational studies and computer simulations. School closures can reduce influenza transmission but would need to be carefully timed in order to achieve mitigation objectives. Travel-related measures are unlikely to be successful in most locations because current screening tools such as thermal scanners cannot identify pre-symptomatic infections and afebrile infections, and travel restrictions and travel bans are likely to have prohibitive economic consequences.

    Recommendations

    Eighteen recommendations are provided in this guideline (Table 1). The recommendations take into account the quality of the supporting evidence, the strength of each recommendation and other considerations. In taking decisions on interventions, each WHO Member State and each local area will need to take into account the feasibility and acceptability of proposed interventions, in addition to their anticipated effectiveness and impact. This guideline provides an overview of relevant considerations.

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Table 1.

Recommendations on the use of NPIs by severity level NPI: non-pharmaceutical intervention; UV: ultraviolet. a A pandemic is defined as a global epidemic caused by a new influenza virus to which there is little or no pre-existing immunity in the human population (1). non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza 4 The most effective strategy to mitigate the impact of a pandemic is to reduce contacts between infected and uninfected persons, thereby reducing the spread of infection, the peak demand for hospital beds, and the total number of infections, hospitalizations and deaths. However, social distancing measures (e.g. contact tracing, isolation, quarantine, school and workplace measures and closures, and avoiding crowding) can be highly disruptive, and the cost of these measures must be weighed against their potential impact. Early assessments of the severity and likely impact of the pandemic strain will help public health authorities to determine the strength of intervention. In all influenza epidemics and pandemics, recommending that those who are ill isolate themselves at home should reduce transmission. Facilitating this should be a particular priority. In more severe pandemics, measures to increase social distancing in schools, workplaces and public areas would further reduce transmission. Experimental studies suggest that hand hygiene can reduce virus on the hands. However, there is insufficient scientific evidence from RCTs to support the efficacy of hand hygiene alone to reduce influenza transmission in influenza epidemics and pandemics. Hand hygiene is an important intervention to reduce the risk of other common infectious diseases; therefore, it should be recommended at all times, regardless of the lack of efficacy against confirmed influenza reported in a number of RCTs. There is also a lack of evidence for the effectiveness of improved respiratory etiquette and the use of face masks in community settings during influenza epidemics and pandemics. Nevertheless, these NPIs may be conditionally recommended for ill persons because of other considerations (e.g. the high cost of face masks), and they are generally feasible and acceptable. It is likely that these personal interventions could be effective if implemented in combination. There is sufficient evidence on the lack of effectiveness of entry and exit screening to justify not recommending these measures in influenza pandemics and epidemics. There is weak evidence, mainly from simulation studies, that travel restrictions may only delay the introduction of infections for a short period, and this measure may affect mitigation programmes, be disruptive of supply chains or be unacceptable to communities for various reasons. There is no evidence on the effectiveness of travel advice; however, given the potential benefits. it is recommended that health authorities provide advice for travellers. Border closures may be considered only by small island nations in severe pandemics and epidemics, but must be weighed against potentially serious economic consequences. This document will serve as a core component of WHO’s influenza prevention and control programme in community settings. The successful implementation of this guideline depends on the inclusion of NPIs as a robust strategic plan at national and local levels, as well as the appropriate application of its recommendations.