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populations, ranging from limits on how or where an individual can travel to full quarantine. Quarantine is a separation of potentially infectious individuals from susceptible populations. It is often confused with isolation, which refers to separating individuals known to be transmissible (typically implemented in a health facility). Though isolation is routinely used in healthcare and public health practice, the use of quarantine is rare and has been controversial. Social distancing covers an array of measures aimed at reducing contact between members of the community that could potentially result in disease transmission, including closing schools, canceling mass gatherings, facilitating remote- or tele-working, and suspending mass transit operations. 57 A multitude of factors will likely determine how effective NPIs will be, such as the size and geographical range of the outbreak, the specific pathogen, the timing of the outbreak, and the country of occurrence. For example, studies have found that travel restrictions would be less effective once a disease has spread to multiple geographic areas or been introduced to large cities. Additionally, studies show that travel restrictions may have some impact for mild to moderately transmissible pathogens (such as SARS).122 For highly transmissible pathogens, travel restrictions may only slightly delay the epidemic peak, and the total number of cases would ultimately experience no significant change.123 While travel restrictions would be unlikely to prevent or substantially slow regional or international transmission of infectious diseases, these measures are commonly used by countries in response to international outbreaks.10,123-127 In recent events such as the 2009 influenza A H1N1 and Ebola in West Africa, many countries implemented travel restrictions, despite evidence that such measures would likely not help. In some instances, these measures have hindered international efforts to contain disease spread.128 In the context of a high-impact respiratory pathogen, quarantine may be the least likely NPI to be effective in controlling the spread due to high transmissibility. To implement effective quarantine measures, it would need to be possible to accurately evaluate an individual’s exposure, which would be difficult to do for a respiratory pathogen because of the ease of widespread transmission from infected individuals. Quarantine measures will be least effective for pathogens that are highly transmissible, have short incubation periods, and spread through true airborne mechanisms, as opposed to droplets. As with travel restrictions, quarantine appears to delay the introduction of highly transmissible diseases but not prevent their spread entirely. Quarantine measures also appear more effective with pathogens that had a longer incubation period, such as measles, compared to those with shorter incubation periods, such as influenza.123 Experiences with quarantine during the West Africa Ebola epidemic highlight the added difficulty of implementing such measures on a large scale, which would only be more difficult in the case of a highly transmissible respiratory disease.129 NPIs often require addressing additional considerations or challenges to implement. For example, quarantine requires strict adherence to be effective, so it works best when government has a trusting relationship with the public. Quarantine and other movement restrictions also involve legal and ethical considerations and should be supported by available evidence to prevent undue burden on affected individuals. The government must have both the legal authority to quarantine individuals and the operational ability to enforce quarantine orders. Other considerations when quarantine is being considered include the responsibility for ensuring the safety of affected individuals that are quarantined and providing medical, communication, and legal services as well as food, shelter, and other necessary supplies. 58 Monitoring and enforcing some of these NPI measures would be quite difficult if not impossible, due to the inability to fully monitor large communities and address noncompliance issues. In pandemic conditions when leaders are under great pressure to act, NPIs could be employed in inappropriate circumstances or have serious secondary or tertiary consequences that could themselves hinder outbreak response efforts. For example, travel restrictions could potentially hinder response efforts, as they could slow or prevent the transportation of personnel or materials. They would place additional economic burdens on the affected country, as the restrictions could hamper or stop their ability to trade. The disruption of normal activities such as schools closing may result in children congregating elsewhere, thus making social distancing efforts irrelevant. Quarantine efforts could be highly disruptive to societies and economies if they are implemented for prolonged periods.121 In the response to government efforts to quarantine apartment complexes in Hong Kong during the SARS response, inhabitants of those buildings fled before authorities arrived, increasing risk of spread and driving the disease underground.130 NPIs would be highly likely to be considered or used by countries during a high-impact disease outbreak for a number of reasons. If there are no available medical countermeasures, NPIs may be viewed as the primary intervention to contain and control the event. NPIs such as travel restrictions have also been employed by countries as a political or social measure to abate fear rather than a necessary public health measure. While national public health guidelines generally recommend NPIs during an outbreak to limit contact frequency between individuals and to decrease the potential risk of spread of respiratory pathogens, there is a broad lack of evidence of efficacy and a lack of understanding about secondary adverse impacts. It is necessary to further study the effectiveness of NPIs in a variety of contexts to ensure that they are employed properly with a strong evidence base, and that the value of taking any specific NPI intervention in a particular pandemic setting is not outweighed by the potential harm. It is important to communicate to political leaders the absence of evidence