“Much of the discussion so far related to the future trajectory of COVID-19 has rightly been focused on the effects of seasonality and non-pharmaceutical interventions [NPIs], such as mask-wearing and physical distancing,” said co-first author Chadi Saad-Roy, a Ph.D. candidate in Princeton’s Lewis-Sigler Institute for Integrative Genomics.

“In the short term, and during the pandemic phase, NPIs are the key determinant of case burdens. However, the role of immunity will become increasingly important as we look into the future.”

“Ultimately, we don’t know what the strength or duration of natural immunity to SARS-CoV-2 – or a potential vaccine – will look like,” explained co-first author Caroline Wagner, an Assistant Professor of Bioengineering at McGill University who worked on the study as a postdoctoral research associate in the Princeton Environmental Institute (PEI).

“For instance, if reinfection is possible, what does a person’s immune response to their previous infection do?” Wagner asked.

“Is that immune response capable of stopping you from transmitting the infection to others?

These will all impact the dynamics of future outbreaks.”

The current study builds on previous research by the same team, published in Science on May 18 that reported that local variations in climate are not likely to dominate the first wave of the COVID-19 pandemic.

In the most recent paper, the researchers used a simple model to project the future incidence of COVID-19 cases – and the degree of immunity in the human population – under a range of assumptions related to how likely individuals are to transmit the virus in different contexts.

For example, the model allows for different durations of immunity after infection, as well as different extents of protection from reinfection. The researchers posted online an interactive version of model’s predictions under these different sets of assumptions.

As expected, the model found that the initial pandemic peak is largely independent of immunity because most people are susceptible.

However, a substantial range of epidemic patterns are possible as SARS-CoV-2 infection – and thus immunity – increases in the population.

“If immune responses are only weak, or transiently protective against reinfection, for example, then larger and more frequent outbreaks can be expected in the medium term,” said co-author Andrea Graham, professor of ecology and evolutionary biology at Princeton.

The nature of the immune responses also can affect clinical outcomes and the burden of severe cases requiring hospitalization, the researchers found. The key question is the severity of subsequent infections in comparison to primary ones.

Importantly, the study found that in all scenarios a vaccine capable of eliciting a strong immune response could substantially reduce future caseloads. Even a vaccine that only offers partial protection against secondary transmission could generate major benefits if widely deployed, the researchers reported.

Factors such as age and superspreading events are known to influence the spread of SARS-CoV-2 by causing individuals within a population to experience different immune responses or transmit the virus at different rates. The study found that these factors do not affect the qualitative projections about future epidemic dynamics.

However, the researchers note that as vaccine candidates emerge and more detailed predictions of future caseloads with vaccination are needed, these additional details will need to be incorporated into more complex models.

The study authors also explored the effect of ‘vaccine hesitancy’ on future infection dynamics. Their model found that people who decline to partake in pharmaceutical and non-pharmaceutical measures to contain the coronavirus could nonetheless slow containment of the virus even if a vaccine is available.

“Our model indicates that if vaccine refusal is high and correlated with increased transmission and riskier behavior such as refusing to wear a mask, then the necessary vaccination rate needed to reach herd immunity could be much higher,” said co-author Simon Levin, the James S. McDonnell Distinguished University Professor in Ecology and Evolutionary Biology and an associated faculty member in PEI.

“In this case, the nature of the immune response after infection or vaccination would be very important factors in determining how effective a vaccine would be.”

One of the main takeaways of the study is that monitoring population-level immunity to SARS-CoV-2, in addition to active infections, will be critical for accurately predicting future incidence.

“This is not an easy thing to do accurately, particularly when the nature of this immune response is not well understood,” said co-author Michael Mina, an assistant professor at the Harvard School of Public Health and Harvard Medical School.

“Even if we can measure a clinical quantity like an antibody titer against this virus, we don’t necessarily know what that means in terms of protection.”

Studying the effects of T-cell immunity and cross-protection from other coronaviruses are important avenues for future work.

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What are non-pharmaceutical interventions?

Non-pharmaceutical interventions (NPI) are public health measures that aim to prevent and/or control SARS-CoV-2 transmission in the community. In the absence of an effective and safe vaccine to protect individuals at risk of severe COVID-19, NPI are the most effective public health interventions against COVID-19.

In most situations, a number of NPI should be implemented simultaneously to maximise effectiveness. NPI such as school and business closures and travel restrictions aim to reduce virus transmission and spread, but they have serious personal, social and economic consequences.

Therefore such consequences need to be foreseen and, where possible, addressed before and during NPI implementation. Achieving sustained public compliance with any NPI is critical for its effectiveness. Therefore any NPI implementation plan should be accompanied by a robust communication strategy.

Since NPI are almost always applied in combinations and at varying levels of intensity, it is challenging to analyse the effectiveness of each measure individually. The assessment of the effectiveness of NPI is based on statistical methods and epidemiological modelling studies, as well as evidence from influenza and other respiratory viruses.

There are three main categories of NPI:

• individual, such as hand hygiene, respiratory hygiene and use of face masks,
• environmental, such as cleaning and ventilation of indoor spaces,
• population-related, such as promoting physical distancing and limiting and restricting movement and the gathering of people.

Widespread, timely testing and contact tracing are cornerstone measures of the response at all stages of the epidemic and underpin NPI measures to isolate cases and quarantine contacts. Testing and contact tracing strategies and operations are covered in detail elsewhere [1,2].

COVID-19 transmission

Evidence currently available indicates that COVID-19 may be transmitted from person to person by several different routes [3]. Infection is understood to be mainly transmitted via respiratory droplets containing the SARS- CoV-2 virus. Transmission through aerosols probably occurs in closed spaces (short-range aerosol), where many people linger for longer periods of time. It is also known to occur in healthcare settings during aerosol-generating procedures (e.g. intubation). Indirect transmission through fomites that have been contaminated by respiratory secretions is considered possible, although so far transmission through fomites has not been documented.

Moreover, the role of other routes of transmission (e.g. faecal-oral or blood-borne) has not been documented.

Asymptomatic transmission (i.e. when the infectious person has no symptoms throughout the course of the disease) is difficult to quantify. Available data, mainly derived from observational studies, vary in quality and seem to be prone to publication bias [4,5]. Mathematical modelling studies (not peer-reviewed) have suggested that asymptomatic individuals might be major drivers behind the growth of the COVID-19 pandemic [6,7]. The infectious period begins at least two days before the onset of symptoms and symptoms can often be mild and non-specific.

Since patients can transmit the disease without symptoms or before they realise they are ill, the isolation of sick people alone is insufficient for controlling the spread of COVID-19.

Table 1. Characteristics of SARS-CoV-2 transmission and relevance for NPI

	Value/description (+ ref)	Relevance for NPI
Main transmission routes	Respiratory droplets (large and aerosols), fomites [3]	Mask wearing, hand and respiratory hygiene, avoid indoor and crowded places
Incubation period	Range: 1-14 days [8-11] Median: 5-6 days	Duration of quarantine Follow-up of contacts
Infectious period	1-2 days before symptom onset 10 days after symptom onset in mild cases, 14-20 days in severe cases [12,13]	Duration of isolation, duration of quarantine
Basic reproduction number	2-4 [14,15]	All NPI
Infectiousness by age	Unclear	School measures
Proportion of asymptomatic cases	30-40% [16,17]	Mask wearing, hand hygiene, avoid indoor and crowded places, testing strategy, quarantine
Transmission by asymptomatic cases	Yes	Quarantine, testing strategy
Risk factors for transmission (personal)	Activities, number of contacts	Physical distancing, hand and respiratory hygiene, contact tracing
Risk factors for transmission (setting)	Close contact, indoor settings, crowding, travel	Physical distancing, mass gatherings, travel restrictions
Risk factors for severity (personal)	Old age, underlying diseases	Protection of vulnerable groups

Key messages

Non-pharmaceutical interventions (NPI) are public health measures that aim to prevent and/or control SARS- CoV-2 transmission in the community. As long as there is no effective and safe vaccine to protect those at risk of severe COVID-19, NPI are the most effective public health interventions against COVID-19.

These ECDC guidelines detail available options for NPI in various epidemiologic scenarios, assess the evidence for their effectiveness and address implementation issues, including potential barriers and facilitators.

General considerations on NPI to control COVID-19

• NPI have played a critical role in reducing transmission rates and the impact of COVID-19 in the European Union, European Economic Area (EU/EEA) and United Kingdom (UK). Until a safe and effective vaccine is available to all those at risk of severe COVID-19 disease, NPI will continue to be the main public health tool against SARS-CoV-2.
• Most NPI can have a negative impact on the general well-being of people, the functioning of society, and the economy. Therefore, their use should be guided by data on the local epidemiological situation, with the overall goal of protecting the most vulnerable individuals in the society.
• Specific recommendations to protect the most vulnerable include enhanced surveillance, comprehensive testing, and intensified infection prevention and control practices in settings that host high-risk individuals, such as long- term care facilities.
• In countries/regions/municipalities/communities where sustained control of SARS-CoV-2 has been achieved, as documented by comprehensive surveillance, NPI can be relaxed, allowing society to function almost normally. Under the current exceptional circumstances, imposing travel restrictions on those coming from countries or areas that have not yet achieved transmission control will probably make a meaningful difference to the SARS-CoV-2 epidemiology within the population.
• In countries/regions/municipalities/communities that experience community transmission, the authorities should ensure that personal NPI are understood and correctly applied by the population. This includes maintaining physical distance in all settings, hand hygiene and respiratory etiquette, and the wearing of face masks when physical distancing cannot be guaranteed. The use of face masks is recommended both indoors (e.g. supermarkets, shops and public transport) and in crowded outdoor settings. In addition, use of face masks should be strongly recommended for groups at risk of developing severe complications if infected (e.g. individuals in older age groups or with underlying conditions) and for those whose occupations bring them into extensive face-to-face contact with the public when there is ongoing transmission.

Decision-makers responsible for implementing population- and/or environmental-level NPI, either at local or national level, should consider the advice/evidence below when deciding on the combination of measures.

Considerations in the event of community transmission

During the SARS-CoV-2 community transmission phase, the following interventions may be considered, irrespective of incidence level.

• Promoting and facilitating physical distancing in all settings is an effective NPI to reduce the levels of SARS- CoV-2 transmission in the community.
• Advising the population to voluntarily self-isolate if experiencing COVID-19 compatible symptoms is an essential measure for reducing the number of secondary infections. This should be linked to easy access to testing and rapid contact tracing, testing of high-risk contacts irrespective of symptoms, and the quarantining of contacts.
• Advising the population to consistently meet with the same people in ‘social bubbles’, whether friends or co-workers, can allow for a greater degree of contact between people, while still minimising the risk of SARS-CoV-2 transmission and associated outbreaks.
• Limiting the size of indoor and outdoor gatherings decreases the likelihood of SARS-CoV-2 spreading to large numbers of people. Such a measure is more effective if implemented consistently, even for relatively small gatherings (e.g. >10 individuals). Additional organisational measures such as event cancellation, postponement or re-arrangement should be considered, depending on the underlying epidemiological situation.
• Promoting teleworking where possible can reduce the risk of outbreaks in the workplace.
• Closing selected businesses, such as places where people have limited possibility for physical distancing, could be more effective than closing all businesses, and therefore is a possible option for reducing transmission while avoiding large-scale economic and social impact.
• Proactive school closure is not recommended as an effective COVID-19 containment strategy at this stage as there is currently little (and conflicting) evidence on the effect it has on SARS-CoV-2 transmission in the community. Firstly, children (18 years and younger) mostly experience a benign clinical course of COVID- 19 and do not seem to have been the main vector of SARS-CoV-2 in the community. Secondly, because the impact of school closure on children’s education, families’ economies, and on society as a whole is significant and well-documented.
• Environmental measures, such as regular cleaning of frequently-touched surfaces and appropriate ventilation of indoor spaces, can lower the risk of disease transmission in the community. Such measures are particularly relevant in healthcare settings to reduce nosocomial transmission and infection of healthcare workers.

Considerations in the event of widespread transmission

During widespread transmission of SARS-CoV-2, when hospitalisation rates, ICU admissions, and/or mortality is increasing, in addition to the NPI above, the following stricter measures can be considered.

• Stay-at-home measures are a last-resort option due to their significant impact on both society and individuals. Targeted implementation, both geographically and temporally, is preferred and can be considered to control outbreaks which are not responding to other measures. Available evidence does not prove that stay-at-home measures are more effective than other measures, such as the closing of (some) high-risk businesses.
• Population-wide testing strategies (testing all individuals, irrespective of symptoms) may be appropriate in local settings with high incidence. Such an approach would enable public health authorities to identify most of the infectious COVID-19 cases at a given point in time (e.g. including pre-symptomatic, pauci- symptomatic, and asymptomatic cases), allowing for their prompt isolation and the interruption of transmission chains. However, the effectiveness/cost-effectiveness of this approach remains unknown and should not compromise the accessibility or timeliness of testing for those who are symptomatic. Without timely analysis and notification to isolate cases, population-wide testing alone would not be effective in reducing transmission.
• Reactive closures of schools may be necessary as a consequence of widespread virus transmission in the community and educational settings. Reactive school and day-care closures will probably not reduce the impact of the epidemic, but may be necessary due to high absenteeism and operational issues, especially if the spread of SARS-CoV-2 coincides with the ongoing influenza season in an EU/EEA country.

Addressing NPI compliance

• Support for NPI has varied considerably across countries and in different population groups within the same country: what works to promote safe behaviour in one city, country, culture, or population may be ineffective or otherwise sub-optimal in another. Several EU/EEA countries have therefore been working to incorporate behavioural insights into their COVID-19 response work, using ongoing assessments of public attitudes, behaviour, and beliefs within their own populations. Innovative means have also been developed for collecting anonymised, aggregated data on people’s movements, which can act as a proxy for compliance with measures (e.g. stay-at-home measures).
• While there is no ‘one-size-fits-all’ approach to promoting NPI compliance, there are nonetheless some key principles that can be applied in all settings, as defined in various theories of behaviour change. The COM- B model is one such theory, based on the common-sense idea that a given behaviour occurs when both the capability and opportunity are present, and when the individual concerned is more motivated to adopt that behaviour than any other. Systematically applying such models can optimise the effectiveness of strategies promoting NPI.

Methodology

The following information sources were used to identify relevant evidence on the effectiveness and implementation of NPI to minimise the spread of SARS-CoV-2:

• Literature review: data from the scientific literature, identified through a structured literature search, was assessed. The search strategy is described in Annex 1.
• ECDC Response Measure Database: a brief descriptive analysis of the implementation of NPI in the EU/EEA and the UK was included. This analysis was taken from the ECDC Response Measures Database which collects information on NPI implemented in EU/EEA countries and the UK since January 2020. The information was extracted on 9 September 2020. Measures by specific countries can be found in the Weekly COVID-19 country overview [18].
• Compendium of relevant ECDC technical documents.

Considerations for implementation

Different compliance levels for various NPI

Substantial evidence has accrued indicating that the imposition of restrictive non-pharmaceutical interventions, such as stay-at-home measures, during the first phase of the COVID-19 pandemic in Europe was associated with increases in loneliness, stress levels and symptoms of depression [19]. Uncertainty about the likely duration of the measures, as well as actual or potential loss of income during this period have been identified as key determinants for these conditions [20,21]. There have also been reports that physical distancing within households where one family member is sick may be seen as socially unacceptable and not always feasible [22]. Further challenges have been encountered when promoting other measures that are perceived as onerous, such as avoiding face touching, disinfecting surfaces, and wearing masks or goggles [23]. All of these psychological and logistical issues may reduce compliance levels with the NPI in question as the pandemic continues to evolve through the northern hemisphere during the autumn and into the winter. By contrast, hand and respiratory hygiene are widely viewed as familiar, actionable, and socially responsible actions to take, and therefore compliance with directives to practice these measures is stronger [22].

Overall, it has become clear that compliance with different COVID-19 NPI varies, with the levels for a given NPI being determined both by people’s outcome expectations (the belief that it is effective) and by their process expectations (the belief that it is not unduly inconvenient) [23].

Challenges to optimising NPI compliance levels

The relaxation of restrictions in most EU/EEA countries over the summer months has, in some people’s minds, created an ambiguity or uncertainty about what actions to take in order to reduce the risk of COVID-19 infection. This uncertainty is in part due to a lack of clarity in some countries about when different NPI should be implemented and when they are not deemed necessary by the authorities [24]. This uncertainty may be complicated further as autumn begins in the northern hemisphere and people return to indoor environments that can facilitate the spread of the virus, and a re-imposition of some NPI should therefore be considered. In some countries, a growing and vocal opposition has emerged to any such re-imposition of restrictive measures, motivated by a range of issues including a desire for a return to ‘normality’, perceptions of a decreased threat from the virus, and broad political discontent from

extremist groups as well as from people protesting at the inequitable socio-economic impact of the pandemic and of the NPI themselves [25-27]. These issues, which have led to large protests in some countries [28], will need to be taken into consideration in any efforts to promote NPI during the autumn and winter months ahead.

An additional challenge to compliance concerns the confusion caused in some people’s minds by the differing recommendations and approaches between and within countries. This makes them question why certain measures may be applied in one country but not in others. One example of this is the difference in approaches between countries regarding travel restrictions and entry requirements, such as screenings at points of entry and quarantine measures. As reported by media in relation to travel during the summer, the variety of measures has been a source of confusion [29]. This situation which, in addition to economic disruption, has also created additional uncertainty for citizens, prompted the EU to call for more clarity and predictability of any measures put in place that may restrict free movement [30].

One of the main challenges in achieving strong compliance with NPI – under any circumstances, let alone the given situation – is that there is no single approach that can be used in all settings and with all population groups [31]. Every government needs to take its own decisions on how to promote compliance with NPI, based on local conditions. Support for NPI has varied considerably across countries and different population groups within the same country. For example, data from a longitudinal multi-country study highlights the substantial variations in face mask usage. In late May-early June, this was lowest among the Scandinavian countries, with fewer than 12% of all respondents from Sweden, Finland, Norway and Denmark stating that they ever wore a face mask when they left the house, compared to 99% in Italy [32]. While face masks were not promoted in Scandinavia at this stage of the pandemic, the data indicate that, for a range of reasons – social, cultural and political factors; trust in the authorities; government strategy, national recommendations and the national and/or local epidemiological trajectory of COVID-19 [33,34] – what works to promote safe behaviour in one city, country, culture, or population may be ineffective or otherwise sub-optimal in another [31].

Principles for promoting compliance to NPI

While there is no ‘one-size-fits-all’ approach, there are some key principles that can be applied in all settings, as defined in various theories of behaviour change. The COM-B model [35] is one such theory, based on the common- sense idea that a given behaviour occurs when both the capability and opportunity are present and when the individual concerned is more motivated to enact that behaviour than any other [36]. This model has been suggested elsewhere as having relevance to the COVID-19 pandemic [37]. In the context of COVID-19 prevention, all three COM-B components (i.e. capability, opportunity, and motivation) have been shown to significantly predict good hygienic practices [38].

The COM-B model is applicable to all of the individual NPI measures discussed in this document. As such, it may be viewed as a useful heuristic technique for decision-makers when planning and assessing the potential efficacy of specific NPI.

Under the umbrella of the three COM-B principles, an array of sub-issues has been identified as being of potential importance for ensuring that NPI promotion strategies are locally relevant, acceptable, and feasible, and thereby of value when promoting compliance:

• Capability

One of the key factors in determining whether and the extent to which an individual has the capability to successfully enact an NPI is their understanding of the NPI in question. To this end, clear, unambiguous and specific guidance on the required behaviour is necessary from the government and other community leaders [23,39]. Some NPI, such as mask-wearing or the use of hand sanitiser, require some sort of material product if people are to be capable of implementing them.

• Opportunity

Authorities and service providers can maximise the opportunities that people have to enact an NPI by a number of means, such as the use of physical markers and channels which can work either at a conscious level or as a sub- conscious ‘nudge’ to encourage certain behaviour. Examples include establishing one-way flows for services and in shops and markets to reduce crowds and limit the number of contacts, or marking out > 1-metre intervals in shops, clinics and other places where it may be necessary to queue, or for desk spacing in schools [40]. Further to the point above on capability, the opportunity for people to comply with recommendations or orders to use products such as face masks or hand sanitiser will be optimised if they are affordable, acceptable, and people know how to use them correctly.

• Motivation

Under the current circumstances, when many people across the EU/EEA are increasingly reluctant to enact NPI as a means of reducing COVID-19 infections, it is particularly important to focus on the means to motivate the population to continue to comply with recommendations. Social norms are core determinants of human behaviour, therefore appealing to longstanding norms (e.g. community solidarity) as means of motivating people may be effective, as well as working to create new norms, such as not shaking hands and staying at home [39,41].

Emphasising the social norms of a specific target group (for example, healthcare workers, young people, the elderly, minority ethnic groups and religious communities) through role models and influencers who are respected by these groups can also increase their compliance to the NPI [41].

A general principle of risk communication is that the promotion of desired behaviour is more likely to lead to higher compliance levels than an emphasis on punishment for perceived breaches [39,41]. Indeed, there are suggestions that messages perceived as authoritarian or moralistic can be counter-productive, particularly where populations perceive unfairness in the management of breaches [39,42]. Enforcement strategies (e.g. mandatory versus recommended) can be important means of motivating people to comply with measures, but mandating NPI may be challenging for law enforcement agencies [43], and in some countries clear recommendations are seen as preferable to the imposition of mandatory measures [44,45].

Connecting behavioural insights with risk communication

Risk and crisis communication is essential for translating the insights gained from behavioural science into messages that are readily understood and accepted by target audiences. An important starting point is seeking to ensure that both behavioural sciences and emergency risk communication are afforded dedicated strategic roles within emergency response structures. Messaging should be consistent across multiple sources, tailored to specific cultural contexts [46], and should provide guidance on specific actions that can be undertaken. Ideally messages should be delivered using a range of media, social and traditional and, when developing messages, it is always best to consult the specific target audience in advance, if possible [46]. The provision of messages to certain communities (for example those who are medically and socially vulnerable) may be facilitated by partnerships with civil society, and may also require community engagement strategies [47,48].

The need for ongoing behavioural research

As indicated above, an overriding principle for promoting compliance with NPI is that what works well in one setting or population group may be ineffective in another. Local conditions and local culture must be taken into account if an NPI strategy is to be acceptable and feasible, and several EU/EEA countries have been working to incorporate behavioural insights into their COVID-19 response work, including through ongoing assessments of public attitudes, behaviour and beliefs [49-51]. World Health Organization’s Regional Office for Europe has also developed a COVID-19 survey tool for use by Member States [52], and this has been in use in Germany since March [53]. Through this work, changes in social norms and expectations in different settings can be investigated, emerging issues (for example, stigma, misperceptions and conspiracy theories) can be identified, and direct feedback can be obtained from the population on current NPI strategies. This will enable a strong foundation to be built for planning and risk communication activities, to ensure that NPI are socially acceptable and feasible.

Cross-country datasets on COVID-19 knowledge, attitudes and behaviour have also been produced, providing useful comparisons of the acceptability and uptake of different NPI over time and in different countries [54]. In addition, innovative means have been developed for collecting anonymised, aggregated data on people’s movement – which can act as a proxy for compliance with measures (e.g. stay-at-home measures) – one example being wearable activity tracking devices [55]. Analysis of Twitter has provided feedback on the public responses to COVID-19 NPI regimes [56], while Google’s COVID-19 Community Mobility Reports give aggregated, anonymised details of daily mobility patterns in communities across the globe which can be used to analyse compliance with stay-at-home and other large-scale NPI [57].

In spite of these advances, there is currently a dearth of evidence on the evaluation of strategies to promote NPI compliance, and strong calls have been made to address this situation [36]. There is also very limited qualitative research in the literature on this subject, even though such an approach could throw important light on issues that may not be amenable to survey-type data, such as providing insights into potential barriers and facilitating factors for compliance with various NPI in different populations.

reference link : Suggested citation: Guidelines for non-pharmaceutical interventions to reduce the impact of COVID-19 in the EU/EEA and the UK. 24 September 2020. ECDC: Stockholm; 2020.

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As of February 28, 2020 the COVID-19 outbreak has caused 78,961 confirmed cases (2791 deaths) across China, with the majority seen in Wuhan City, and 4691 cases (67 deaths) reported in the other 51 countries.1 Further spread has occurred to all populated continents of the World, with many anticipating that a pandemic is approaching.2,3

As an emerging disease, effective pharmaceutical interventions are not expected to be available for months,4 and healthcare resources will be limited for treating all cases. Nonpharmaceutical interventions (NPIs) are therefore essential components of the public health response to outbreaks.1,5-7

These include isolating ill persons, contact tracing, quarantine of exposed persons, travel restrictions, school and workplace closures, and cancellation of mass gathering events.5-7 These containment measures aim to reduce transmission, thereby delaying the timing and reducing the size of the epidemic peak, buying time for preparations in the healthcare system, and enabling the potential for vaccines and drugs to be used later on.5

For example, social distancing measures have been effective in past influenza epidemics by curbing human-to-human transmission and reducing morbidity and mortality.8-10

Three major NPIs have been taken to mitigate the spread and reduce the outbreak size of COVID-19 across China.11,12 First, inter-city travel bans or restrictions have been taken to prevent further seeding the virus during the Chinese new year (CNY) holiday.

People in China were estimated to make close to 3 billion trips over the 40-day CNY travel period from January 10 to February 18, 2020.12,13 A cordon sanitaire of Wuhan and surrounding cities in Hubei Province was put in place on January 23, 2020, just two days before CNY’s day on January 25.

However, Wuhan’s lockdown is likely to have occurred during the latter stages of peak population numbers leaving the city before CNY, with around 5 million people likely leaving before the start of the travel ban, departing into neighbouring cities and other megacities in China.14 Since CNY’s day, travel restrictions in other provinces were also put in place across the country.

The second group of containment measures involves improving the screening, contact tracing, identification, diagnosis, isolation and reporting of suspected ill persons and confirmed cases.11 Since January 20, particularly in Wuhan, searches for cases, diagnosis and reporting have sped up across the country.

Local governments across China encouraged and supported routine screening and quarantine of travellers from Hubei Province in an attempt to detect COVID-19 infections as early as possible. In Wuhan, where the largest number of infected people live, residents were required to measure and report ther temperature daily to confirm their onset, and those with mild and asymptomatic infections were also quarantined in “Fang Cang” hospitals, which are public spaces such as stadiums and conference centres that have been repurposed for medical care.11

The average interval from symptom onset to laboratory confirmation has dropped from 12 days in the early stages of the outbreak to 3 days in early February, highlighting how the efficiency of disease detection and diagnosis has greatly improved.15,16

Third, inner-city travel and contact restrictions were implemented to reduce the risk of community transmission. This involved limiting individual social contact, using personal hygiene and protective measures when people needed to move in public, and increasing the physical distance between those who have COVID-19 and those who do not.11

As part of these social distancing policies, Chinese government encouraged people to stay at home as much as possible, cancelled or postponed large public events and mass gatherings, and closed libraries, museums, and workplaces.17,18

Additionally, to fully cover the suspected incubation period of COVID-19 spread before Wuhan’s lockdown, the CNY and school holidays were also extended, with the holiday end date changed from January 30 to March 10 for Hubei province, and Feb 9 for many other provinces.19-21

The implementation of these NPIs has coincided with the rapid decline in the number of new cases across China, albeit at high economic and social costs.15,16 On February 17, the State Council required localities to formulate differentiated county-level measures for precise containment of the COVID-19 outbreak and the restoration of socioeconomy affected by the outbreak.22

The timing of implementing and lifting interventions is likely to have been and continue to be important, to take advantage of the window of opportunity to save lives and minimize the economic and social impact.23,24

The increasing numbers of cases of COVID-19 outside China and establishment of secondary transmission in multiple places highlights its pandemic potential. The best available scientific evidence is therefore required to design effective NPI strategies and disseminate this knowledge urgently to help policy makers assess the potential benefits and costs of NPIs to contain COVID-19 outbreaks.

Some previous studies have preliminarily explored the lockdown of Wuhan,25-27 travel restrictions,28-30 airport screening,31,32 and the isolation of cases and contact tracing for containing virus transmission, respectively.33,34 The conclusions of these studies are persuasive, there are still key knowledge gaps on the effectiveness of different interventions.15

To fully justify the preparation, implementation, or cancellation of various NPIs, policy makers across the World need evidence as to the combination and timings of each, which remains lacking.

Based on near-real time human movement and disease data, here we conducted an observational and modelling study to develop a travel network-based modelling framework. We aimed to reconstruct COVID-19 spread across China and assess the effect of the three major groups of NPIs mentioned above. Given the expanding landscape of epidemics across the World, our findings contribute to improved understanding of the effect of NPI measures on COVID-19 containment and can help in tailoring control strategies across contexts.

reference link : : https://doi.org/10.1101/2020.03.03.20029843

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More information: Chadi M. Saad-Roy et al, Immune life history, vaccination, and the dynamics of SARS-CoV-2 over the next 5 years, Science (2020). DOI: 10.1126/science.abd7343