Factors impacting social distancing measures for preventing coronavirus disease 2019 [COVID-19]: A systematic review

Background: Social distancing measures (SDMs) protect the health of the public from coronavirus 2019 (COVID-19) infection. However, the impact of SDMs has been inconsistent and unclear. This study aims to review the factors impacting SDMs (e.g. isolation, quarantine) for reducing the transmission of COVID-19. Methods: A systematic review was conducted. We searched MEDLINE, EMBASE, Allied & Complementary Medicine, COVID-19 Research and WHO database on COVID-19 for primary studies assessing the enablers and barriers associated with SDMs, and reported in accordance with PRISMA statement. We used JBI Critical Appraisal Checklist for the cross-sectional survey and Qualitative Research to assess the methodological qualities and synthesised performing thematic analysis. Two reviewers independently screened the papers and extracted data. Results: A total of 1235 citations were identied, of which 16 were found to be relevant. The studies reported in two broad categories, under seven separate themes: positive impact of SDMs, effective public health interventions, positive change in people’s behaviour, worries and concerns about COVID-19, roles of mass media, physical and psychological impacts, and ethnicity/age associated with COVID-19. Conclusion: The identied evidence signals that SDMs are generally effective for preventing or reducing transmission. There is a scope and need to nd the best methods and approaches at the primary healthcare level in terms of developing objective measures and interventions to establish the link between different factors and SDMs and reducing transmission of COVID-19 trend effectively, eciently and equitably. “social distancing”, “quarantine”, “patient isolation” EMBASE, COVID–19 COVID–19. following “social distancing measures”, “social distancing”, “quarantine”, “patient isolation” combined with Primary search were SDMs (all synonyms) and COVID–19 (all synonyms) using searching’—searching for (MeSH, EMTREE) searching’, Boolean operators useful to COVID–19 resources, this dicult and time-consuming and the systematic search strategies noted lack of specicity.

physical interventions for reducing the spread of respiratory viruses, and found no evidence regarding screening at entry ports and social distancing [31]. Lewnard and Lo [7] and Michigan Medicine Projections [32] reported that combined SDMs or interventions using social isolation, quarantine, school closure, and workplace distancing appeared effective in reducing COVID-19 compared to no interventions at all. This approach, however, reported considerable challenges, e.g. societal disruption, social isolation/rejection, mental stress and psychological trauma, lack of tests and testing facilities, poor contact tracing, lack of surveillance. None of these studies examined the SDMs factors in reducing the transmission of COVID-19 systematically. This systematic review aimed to examine the factors impacting SDMs for preventing  Review question What has been the impact of social distancing measures for preventing coronavirus disease 2019 ?

Methods
We conducted a systematic review (SR) to review relevant research literature, using systematic and explicit, accountable methods, to answer a speci c research objective [33].
Criteria for considering studies for review Inclusion criteria 1. Primary research describing SDMs, e.g. social distance, isolation and quarantine across all age-sex groups.
2. Research reporting enablers and barriers to implementing SDMs, e.g. social distance by avoiding crowds and restricting movement, isolating ill people and quarantine of exposed people for preventing transmission or controlling the spread of COVID-19 infections as outcome measures.

Articles published in
Authors developed a detailed study protocol with speci c searching terms and strategies (Additional le 1). We utilised the 'Related Articles' including the best match and most recent features in PubMed. Searches were also supplemented by reviewing the reference lists ('references of references') of selected articles to nd any other relevant papers. We contacted subject experts/information specialists from authors' Universities to verify the research strategy, ensuring its comprehensiveness. We also contacted some study authors to identify the additional studies. The literature search was conducted during May-June 2020 and the last search was conducted on 8 June 2020 in order to contemplate the recent pandemic crisis. The searchers were not limited by study design or study location.

Selection of studies
The citations identi ed through the searches were imported into Mendeley Reference Manager (https://www.mendeley.com/). All studies emerging from the databases have been screened twice: i) screening of abstracts and titles against minimum inclusion criteria, and ii) review of full text. We used the standard PRISMA ow diagram to provide the process of study selection [34] (Fig. 1). We also completed PRISMA checklist for this manuscript (Additional le 2).

Quality appraisal of included studies
We used JBI Critical Appraisal Checklist for the cross-sectional survey [35] and Qualitative Research [36] to assess the methodological qualities. All included studies were assessed by two reviewers (KR, CML) using the standardised eight and ten questions 4-item checklists i.e. Yes, No, Unclear and Not Applicable (Additional le 3) and the results have been used to inform synthesis and interpretation of the ndings. To facilitate comparison of appraisal processes, all reviewers recorded the rationale for inclusion or exclusion, and discrepancies were discussed and resolved by consensus.
Data extraction, analysis and synthesis Studies in this review were not su ciently homogenous to analyse using meta-analysis [37]. Therefore, results are summarised using narrative synthesis and tabular form using thematic analysis ( Table 2). Data extracted using the following summary data: sample characteristics i.e. study aim, study location, study design, sample size, and appraisal checklist(s) and the overall reviewer comments. Thematic analysis/synthesis was used to identify the important or recurrent themes and the ndings are summarised thematically [38]. Coding process and the development of themes were discussed among authors.

Results
The search results are summarised in Figure 1. In total, 1235 citations were identi ed, of which 16 were found to be relevant [39,40,  In general, these studies cover one or more of two areas: i) positive impacts (enablers) of SDMs for COVID-19, and ii) speci c barriers to control or reduce transmission of COVID-19. Eight important themes under two broad descriptive themes emerged (Fig. 2). The relative contribution of each study to the synthesis is in Table 2. *Numbers in this column signify the quality criteria from the critical appraisal checklist (Additional le 3) that studies were deemed to have met.  [39,40,46,54].
One study has highlighted that: Without strengthening SDMs, local infections are likely to continue occurring, given that the effective reproduction number (R o) is approximately 1 or slightly higher. Travel measures and testing, tracing, and treating efforts are particularly important in maintaining suppression, although these measures will be increasingly di cult to implement as case numbers increase [40].
Similarly, other studies further added that if the basic reproduction number of COVID-19 in Hong Kong, UK and US exceeds 2, (it was 2·2 in Wuhan), we would need >44% reduction in COVID-19 transmission to completely avert a local epidemic. A reduction of this magnitude could, however, substantially atten the peak of and area under the epidemic curve, thus reducing the risk of exceeding the healthcare system capacity, potentially saving many lives, especially older adults [39,40,42,44,51].
Studies reported that quarantine, and school and border closure have been the most effective means of suppressing transmission [40,43] The extracts below illustrate this: The package of public health interventions (including border entry restrictions, quarantine and isolation of cases and contacts, and population behaviour changes, such as social distancing and personal protective measures) that Hong Kong has implemented since late January, 2020, is associated with reduced spread of COVID-19 [40, p. p. e284].
The study participants reported frequent use of sanitizers, hand wash, and masks during the past week. This indicates participants' increasing concern towards personal hygienic measures. Awareness about COVID-19 is re ected in behaviour and attitude as most participants agreed with social distancing, avoiding travel, self-quarantine and adequate hygiene [48, p.4].
Theme 3: Positive changes in people's behaviour We found four studies (of 16) reported SDMs in uenced people's behaviour [39][40][41]53]. Atchison et al. [39] reported that part of the success in early February 2020 was changing people's behaviour to comply with government actions.
The extracts below illustrate this: Social distancing and population behavioural changes with social and economic impacts less disruptive than total lockdown can meaningfully Most participants felt that guidance on social distancing and isolation had been generally unclear, although some described how it had "become clearer". Many participants exhibited lack of trust in government or in the media [42, p.12].

Theme 5. Debatable role of mass media
Two of 16 studies identi ed this as a barrier [45,52]. These studies found that rumours in social media, and electronic and print media during SDMs (isolation, self-quarantine), and total restriction of travel (curfew) were associated with negative impact on mental health as they constantly depict the pandemic and deaths related to it. Therefore, people become angry, restless, worried, have di culty coping, and feel emotionally exhausted [52].
One study observed that: Approximately 28% of people report sleep di culties. More than two-thirds of participants reported themselves worried after seeing posts about Theme 6: Physical and psychological impacts Four of the 16 studies identi ed these barriers [42,45,47,52]. The commonest associated factors were: anxiety [47], increased time in quarantine associated with post-traumatic stress disorder, depression [47], decrease in physical activity [45], loss of social interaction, and emotional and psychological distress [42].
The extracts below illustrate this: The mandated lack of social and, especially, physical contact with family members were identi ed as particularly di cult. Con nement at home and work, being unable to see friends, being unable to shop for basic necessities of everyday life, and being unable to purchase thermometers and prescribed medications enhanced their feeling of distance from the outside world [47, p.10].
All participants felt that the social distancing and isolation polices had had signi cant social and psychological impacts on their lives and the central theme was loss […]. These emotional and psychological losses were particularly acute for those living in more urban, densely populated cities like London or Birmingham. They were also especially evident amongst those in low-paid or precarious occupations, who had either lost their job or income or were now relying on parental, familial or state nancial support as a result of the pandemic [42, p.10].
The extracts below illustrate this: More disadvantaged backgrounds were less likely to be able to work from home or self-isolate if needed, suggesting structural barriers to adopting preventive behaviours in these groups. The most economically disadvantaged in society are less able to comply with certain NPIs, likely partly due to their nancial situation [39,p.17].
Adoption of SDMs was almost twice as likely in people over 70 compared to adults aged 18 to 34. Notably, those that were single were less likely to practise social distancing. There was a strong association between socio-economic deprivation and ability to adopt NPIs [39,p.15; 43,p.6]. Fig. 3 is a conceptual framework (CF) that emerged from this study, which shows the interconnection of SDMs, factors and reducing COVID-19. To make the effective link between them, all these components are essential; putting people at the centre of the framework, ensuring their needs are appropriately met by providing best-quality care. As the rst point of contact for patients or users, primary healthcare would play a key role. The approach would also help to reduce the basic reproduction number (R o) to avert a local epidemic and atten the peak of and area under the epidemic curve. R o is considered a key indicator to assess "whether a pathogen introduced into a community will spread and, signi cantly gives guidance as to its rate of spread" [53,p.2]. Generally, it is expected to be below 1.0. This CF also acknowledges the capacities and capabilities of primary healthcare systems, health inequalities, social determinants of health, including the capacity of the national laboratory system that appropriately followed the WHO's mantra of "trace, test, and treat" to suppress and control the coronavirus epidemic [8,11]. Similarly, CF recognises societal norms, culture and values, as each country has its own speci c geo-socio-economic, political, legal and cultural contexts. In this study, we found major factors, enablers or barriers, impacting SDMs emphasising the positive roles of SDMs, public health interventions, behaviour changes, people's worries and concerns, myths and stigma and physical and psychological impact including the debatable role of media. Similar issues have been documented in different literatures [54,55]. The purpose of social distancing is to inhibit the intensity of transmission (R o) to reduce R o to <1 or "contain the outbreak within a manageable duration" [56, p.2]. The ultimate strategy is to slow down or curb the spread of the overall disease burden-morbidity, severity, fatality, health complications and socio-economic consequences-and reduce the impact on health services. Anxiety or worries about the duration of quarantine have been highlighted in this study. A similar issue has also been reported in previous studies. Sjödin et al. [56], for example, based on the experience of the COVID-19 outbreak in Italy, discussed that for an average household of three persons, approximately 30-54 days will be enough quarantine with near-complete and medium adherence community quarantine adherence respectively, assuming 10% asymptomatic infections. In this case, seven secondary cases would be expected in a population of 5000, or 70 secondary infections in a population of 50,000, assuming 10% asymptomatic infections.

Discussion
This study found that social distancing has been effective only if integrated with enhanced personal hygiene, environmental sanitation and adequate and appropriate use of PPE (use of masks, handwashing, coughing etiquette). Early diagnosis and prompt management of con rmed cases by isolating (physical distance), timely follow-up and quarantine recommendations (14 days) for close contacts of a case constitute the CORE of COVID-distance to the individual infected and the type of face mask and eye protection worn. From a policy and public health perspective, current policies of at least 1 m physical distancing seem to be strongly associated with a large protective effect, and distances of 2 m could be more effective". ECDC report [57,p.3] highlighted that: "The success of social distancing measures that are implemented over an extended period may depend upon ensuring that people maintain social contact-from a distance-with friends, family and colleagues" as well as the strictness of quarantine adherence, household size, and highest rates of compliance [53,56]. Similar issues have also been reported by the ndings of our study.
However, very little was known on our speci c research question on the extent and the factors impacting SDMs in reducing transmission of COVID-19 nationally and globally, as there were no previous systematic reviews on this subject, or commentaries examining the factors associating SDMs and COVID-19. There are, however, some rapid reviews, summaries and mathematical modelling studies covering COVID-19, in China, South Korea, UK, USA, and other countries, but the literature has not been systemically reviewed or synthesised. Similarly, the implementation of social distance differs by country due to the wide range of predictors associated with this measure, some far more strict than the UK, with Sweden at the opposite end of the spectrum. Therefore, it is di cult to assess which speci c SDMs or measures would have a higher impact on the effects of social distancing to reduce transmission.
Lack of awareness and misconceptions about COVID-19 and the physical and psychological impacts due to lockdowns have been reported in the included studies, and similar ndings were reported from previous studies [58]. Therefore there is a need to intensify awareness, education and campaigns, targeting general and speci c spheres of populations, utilising internet-based information, use of social in uencers, education and counselling (IEC) strategies to correct these misconceptions and provide support by different stakeholders (governments, NGOs, charities, national volunteers, community support groups). Increased media coverage would be one key strategy to make SDMs successful [46,52,57].
In this study, we also found compliance has been one important factor, but it was not easy for securing public compliance in liberal democratic societies. Similarly, the approach in authoritarian regimes, e.g. China, would likely be unacceptable in other parts of the world. Related to this is how long restrictive measures can be tolerated, which lacks solid evidence [56,59]. Moreover, social distancing becomes a highly charged topic creating a lieu of debate among the politicians, economists, medical and public health professions. The likelihood is that COVID-19 will become endemic, which suggests long-term behavioural adjustments as reported in our study [45]. Similarly, we argued that social distancing is not part of the culture in either developed or developing countries, for different reasons [60]. In developing countries, it is more related to population density, crowding, workplace conditions etc., such as overcrowding in public transport. In developed countries such as Switzerland, people were still following Swiss kiss as late as 20 March, when COVID-19 was already peaking. Similarly, our study found a relationship between social distancing and economic aspects: poverty, living in slums etc. in developing countries; marginalized populations in developed countries. A similar issue has also been reported in the previous studies [61][62][63]. Therefore, there is a need to completely change the way the economy, businesses, and life are organised to protect the vulnerable groups such as homeless, disabled, undocumented migrant workers and inmates. Similarly, home life should be looked at, as evidence suggests we need to change the way we interact at home, for example, with vulnerable family members-elderly, pregnant, immunocompromised due to chronic disease or protracted illnesses, at least until the pandemic is over, e.g. curbing the possibility of transferring the disease to the elderly.
Moreover, we found that due to lockdown, people lost their jobs affecting their income and suffered job insecurity in general, but it disproportionately affects the most disadvantaged populations. These ndings are consistent with the previous studies [2][3][4]. A recent descriptive review of data on disparities in the risk and outcomes from COVID19 in the UK has reported that: "The largest disparity found was by age. Among people already diagnosed with COVID19, people who were 80 or older were seventy times more likely to die than those under 40. Risk of dying among those diagnosed with COVID-19 was also higher in males than females; higher in those living in the more deprived areas than those living in the least deprived; and higher in those in Black, Asian and Minority Ethnic (BAME) groups than in White ethnic groups" [3,p.4].
Marmot et al. [64] also argued that: "There are clear socioeconomic gradients in preventable mortality. The poorest areas have the highest preventable mortality rates and the richest areas have the lowest" (p.13). Finally, this study along with other evidence suggests that our health systems have not been proactive enough to cope with the current pandemic [54]. We argue that public health has failed to convince politicians to take rapid action on prevention of spread or prepare for necessary treatment arrangements. These ndings are consistent with those of Pollock et al. [65] and Regmi et al.
[66] and they found that the "structure and capacity of our depleted healthcare system are now largely driving the response to this epidemic" and most likely "it will continue to do so until services that support local communicable disease control are rebuilt and reintegrated".
This study adds to the literature on highlighting the major enablers and barriers of SDM in controlling COVID-19 in public health policy and interventions: i) given the fact that there is no vaccine or treatment available at the time of writing, and ii) there have been limited robust published studies of SDM success factors, with most studies exploring the process rather than hard or tangible outcomes. This scarcity of empirical studies demonstrates the practical realities, e.g. factors or outcomes of SDM would be appropriate for policy-planners, researchers and decision-makers to make it effective.
Strengths and limitations of the review To our knowledge, this study might be the rst systematic review to examine the enablers and barriers impacting SDMs to reduce transmission of COVID-19. It used a systematic and rigorous search strategy developing a systematic review protocol. This study has proposed a conceptual framework (CF) embedding an enablers, barriers and possible outcomes (EBO) con guration, putting people at the centre of the process, making sure that primary healthcare services are accessible to all (Fig. 3). This study also highlighted the themes from the interpretative synthesis and relative contribution of each study (Table 2). This CF has also recognised that the effectiveness of SDMs will depend on the credibility of public health authorities, and on strong leadership and commitment from political leaders and institutions.
This review has, however, several limitations. First, as it was not externally funded, and therefore time and resource were constrained and unable to include and review grey literature. Second, studies are variable in sample size, quality and population, which are open to bias, and the heterogeneity of data precludes a meaningful meta-analysis to measure the impact of speci c enablers or barriers, therefore the ndings warrant generalisation.
Third, despite the overall satisfactory methodological quality of the included papers, methodologies were poorly reported (mostly those preprintspostings in MedRxiv), lacking comprehensive strategies for sampling and procedures, and lacking detail in data gathering and analysis, including identifying and dealing with possible confounding factors (Table 1).
Wolkewitz and Puljak [67] further warned that: "there are many methodological challenges related to producing, gathering, analysing, reporting and publishing data in condensed timelines required during a pandemic." Finally, searching "social distancing" in different databases produced no results.
We noticed that the problem of searching for SDMs and COVID-19 studies was mainly due to rapidly-growing COVID-19 studies in PubMed and other search interfaces, which are not visible in the major search databases (PubMed, EMBASE) due to i) indexing, and ii) often bibliographic databases failed to capture preprint and unpublished studies including registered clinical trials [68,69], and the majority are commentaries, news, perspectives or opinions [67]. Though Shokraneh [68] provided some useful links speci c to COVID-19 resources, still we found this di cult and time-consuming and the systematic search strategies noted lack of speci city.

Directions for Future Research
It is important to determine whether we should look to determine to develop herd immunity. If that is the case then "how can one determine how much herd immunity is su cient to mitigate subsequent substantial outbreaks of COVID-19?" [70]. In addition, many frontline healthcare professionals are dying from COVID-19 and so research needs to nd out why and how ethnicity, migrant status, health inequalities and social determinants of health (SDH) have links with COVID-19 [2,50,71]. It would also be bene cial to see the reasons why children and young people are least affected [72], why some patients develop more serious complications than others [57,(73)73], why do some COVID-19 patients infect many others, whereas most don't spread the virus et all? [74], and what has been the impact of different public health policies and efforts for COVID-19 by gender and age [75].
Similarly, we also need to determine whether the mass testing of antibody status would guide how extensively and how long social distancing should be implemented in a speci c area [28,70], and whether the term 'spatial distancing' would be more appropriate than 'social distancing measures' while addressing the issue of distance between individuals or objects [76]. Finally, we need to know what appropriate quarantine measures would be appropriate in the long run to curb importation of transmission, and whether " attened epidemic curve [will] rise again once we come out of the quarantine adopted worldwide" [28].

Conclusion
The current systematic review highlights the importance of SDMs in the context of global uncertainty. This study provides useful factors-enablers and barriers-to implement and deliver SDMs policy in reducing transmission of COVID-19 and improving health and wellbeing. From this study, the identi ed evidence signals that SDMs are generally effective for preventing or reducing transmission. Based on the results of this study, we consider that targeted approaches alongside social distancing might be the way forward and more acceptable: reduce infection rate to make large-scale testing logistically viable, contact tracing, compliance rate, duration of measures, isolation for positive cases and teams to carry this out. Globally, health systems now, more than ever, face major challenges as they not only need to deal with unwell people but also continue to deliver public healthpreventive measures. The best solution for a health system under pressure is to strengthen primary health care by assessing these factors in future monitoring/evaluation. Further research may be warranted to nd the best methods and approaches in terms of developing objective measures and interventions to establish the link between different factors and SDMs (as a secondary outcome) and reducing transmission of COVID-19 trend (as a primary outcome) effectively, e ciently and equitably.

Abbreviations
Ethics approval and consent to participate Not ethics approval or consent to participate was required.

Consent for publication
The authors give consent for publication of this manuscript Themes identi ed across studies of social distancing measures and COVID-19.