Causal loop diagram: Dynamics of infection
Though there is still debate on whether SARS-CoV-2 spreads via aerosols, the virus has resulted in what is known as the COVID-19 pandemic; in this regard, it is certain that SARS-CoV-2 spreads during close interpersonal contact [11]. In fact, the dynamics of COVID-19 transmission have successfully been described through the use of models showing that infections are spread during such exposure, especially among susceptible populations [12]. Further, asymptomatic carriers can still transmit the virus [13]. Here, transmission efficiency may be affected by a variety of factors, including travel [12] and population density [13][15][16][17]. In sum, the current literature shows that human-to-human contact is a determinant of transmission. As such, the course of infection (including the role of asymptomatic carriers) was featured in the causal loop.
Causal loop diagram: Reviewing the basis of Japanese NPI
Regarding those implemented in 2020, Japanese NPIs can be categorised on the basis of need, including mild tiered interventions (raising sanitation awareness, physical distancing, encouraging remote work and staying home), focused NPIs in high-risk settings (suspending night services for bars and restaurants), and strong NPIs in more severe cases (strongly asking people to remain home, temporary business closures, according to administrative order) [18]. Milder NPIs were implemented during the early phase of the domestic outbreak in February 2020, at which time behavioural requests were issued, such as remembering to wash hands and covering the mouth when coughing [4]. More stringent requests were introduced in March 2020, when individuals were advised to avoid crowded locations [6]. Later on, stronger NPIs were implemented based on a declared state of emergency, with key factors including disease severity, uncontrollability, and the potential of overwhelming hospitals. Stricter measures were also implemented based on the particular severity of COVID-19 in serious cases. In this regard, the spread of the disease inevitably entered an uncontrollable phase due to the silent nature of transmission and moderate reproduction rate. This also resulted in a shortage of hospital beds. As of April 2020, only 12,500 beds were available for those with novel infectious diseases in Japan, accommodating approximately 10,000 patients at the time [13]. The surge of COVID-19 infections thus impelled the Japanese government to declare a state of emergency, at which time hospital capacities were increased [14]. There were also concerns about the possible need to accept additional patients during subsequent epidemic phases, thereby putting health systems in further danger. Ultimately, a second state of emergency was declared in January 2021 as Japan entered the next wave of the pandemic.
It is generally understood that NPIs may negatively affect the economy due to restricted mobility, especially during lockdowns [19]. In Japan’s case, economic countermeasures were targeted at the travel industry, which was expected to benefit from anti-epidemic prioritisation in the NPI context during July 2020, when the number of patients in Tokyo (the most densely inhabited area) indicated the existence of a second viral wave [18]. This is evidence of how the economic sector may pressure the government to forego stronger NPI measures in times of crisis.
Based on the above, we considered that hospital bed shortages were key factors for inducing strong NPIs. On the other hand, we believed that concerns over economic stagnation would serve as negative feedback to stricter NPIs. As part of its public health policy, Japan’s virus testing operations are focused on potential and identified clusters rather than mass testing; this is also a component of an active epidemiological survey [20]. In this regard, it would be adequate to consider that identifying virus carriers either by mass-oriented or focused approaches will help quarantine.
Causal loop diagram: Behavioural effect on transmission and triggering behavioural change
Among the various behavioural measures taken to avoid viral transmission, a system review has suggested the particular efficacy of physical distancing and the usage of face masks [11]. In Japan’s case, previous studies have investigated behavioural changes during the very early phase (February 2020), thus highlighting the positive initial response triggered by mass-media reports of substantial infections incurred on a cruise ship, in which case the ministry’s order to close schools was well-observed [21][22]. Further, an online survey conducted by the LINE Corporation and Ministry of Health and Welfare revealed behavioural changes in which individuals were more willing to avoid crowded locations as soon as Japan declared a state of emergency (April 2020) [23]. Based on these episodes, it would be adequate to consider that behavioural changes are induced via mass-media reports on disease threats and the need for strong NPIs.
Causal loop diagram: People flow
People flow refers to intercommunity human contact and can thus play a significant role in disease transmission, particularly in crowded areas. This is especially pertinent in Japan, which contains several cities with high population densities [5]. As such, we investigated the dynamics of people flow using data provided by Agoop, which is a big data company that collects location information related to people flow through smartphones [24].
For example, we examined the time course of people flow at Shinjuku Station in Tokyo, which is known for facilitating the largest number of commuters in Japan (as many as 250,000). People flow first decreased in March 2020, just after the ministry directed school closures. There was a drastic decrease in April 2020, when the stay-at-home request was issued. Figure 2 shows changes in the number of people at 18:00 on weekdays, which is considered the peak both around and within Shinjuku Station; this represents people flow during the typical commuting time in the Tokyo Metropolitan area. Even after the stay-at-home request was lifted, people flow was found to be at considerably lower levels when compared to pre-pandemic numbers. This shift to lower levels may indicate a general transition to a ‘new-normal’ lifestyle (e.g. remote work or behavioural changes in which people remain home or avoid visiting crowded locations due to long-term concerns about COVID-19). In this context, we constructed quantitative models to test the hypothesis that people flow in crowded places can affect disease transmission. This is described in more detail later in the manuscript.
Causal loop diagram: Customer visits and eWOM
To understand how NPIs affect the restaurant industry, we analysed data on actual customer visits and eWOM communications from Retty Inc., which runs an integrated web-based e-WOM and restaurant reservation service [25]. Both monthly metrics were taken from the year 2020 and normalised on the basis of the previous year. In short, results suggested that customer visits and eWOM (together with people flow) decreased because of COVID-19 in both March and April 2020, with further possible effects from the stay-at-home request issued in April 2020 (Figure 2). All three metrics were similarly affected by these events. Using monthly data from March to September 2020, the correlation coefficient between people flow and customer visits was 0.916, while that between people flow and eWOM was 0.879.
Further, the move in eWOM communications was slower than the shift in customer visits during the pandemic phase from March 2020 to May 2020 (includes the stay-at-home request). This suggests that, although eWOM follows customer visits, there is a delay in outcomes during crisis-driven circumstantial changes. Another hypothesis is that eWOM is resistant to pandemic crises because of the remote nature of the information transmission.
In general, we found that eWOM communications and customer visits were similarly affected by initial information and interventions related to COVID-19; indeed, full recovery was not observed for six months (October). This suggests that the pandemic has had long-term effects on public consciousness.
In sum, eWOM did not appear to affect customer visits in Tokyo based on the abovementioned time course dynamics. Rather, there was a tendency in which eWOM followed customer visits during the first pandemic wave. Although previous reports have shown that eWOM affects sales [10], most such findings are based on cross-sectional observations without clarifying specific conditional dynamics. This suggests the need for additional research once time-course data have been collected under various conditions.
Constructing an integrated causal loop diagram
Based on the information above, we constructed a causal loop diagram depicting the general situation for COVID-19 transmission in the context of Japanese NPIs, including the drawbacks (Figure 3A). Several feedback loops are present in the diagram. As for disease infection, COVID-19 transmission showed a reinforcing nature during the disease spreading phase (Figure 3B, upper); theoretically, herd immunity also appeared to decrease the transmission rate (Figure 3B, lower). On the other hand, the medical collapse loop illustrates the inadequacy of utilising herd immunity as a political strategy (i.e. allowing infections) (Figure 3C, lower), specifically showing that such practices are likely to result in uncontrollable transmission rates and insufficient medical treatments; in turn, this leads to a considerable increase in the death rate. Active epidemiological survey, which is a focused investigation on the circumstances of infection related to patients found, including virus testing of people contacted with patients [26] would partially decrease the transmission rate (Figure 3C, upper). As shown in Figure 3D, appropriate balancing dynamics and the strength of NPIs both decrease when the infection rate decreases. In contrast, the lower portion of Figure 3E shows negative feedback to strong NPIs based on economic stagnation, which can result in the premature termination of NPIs from a public health perspective. Finally, the upper portion of Figure 3E shows the effects of eWOM. Previous research has clarified that increased eWOM is related to better sales [10]. In this study, we hypothesised there would be a short-term increase and decrease of eWOM mass in relation to sales.
While the nature of the 2020 pandemic has highlighted the need to prevent hospitals from becoming overwhelmed, there is still some reticence towards stronger NHIs, which can lead to economic stagnation. By contrast, delayed NHI implementation may worsen the COVID-19 mortality rate [16]. Practically speaking, a large number of hospital beds will be occupied for longer durations than normal, which puts serious pressure on hospital management. These conditions further emphasise the need to adequately time the implementation of appropriate NHIs. In this study, we investigated the issue by conducting a quantitative simulation, which is described in the following sections.
Quantitatively modelling the disease transmission dynamics
According to our model, disease transmission was accomplished via interpersonal contact, which was affected by both people flow and protective behaviour. Here, we assumed that people flow was affected by pandemic consciousness, stay-at-home requests, and new-normal lifestyle effects (Figure 4).
Short-term pandemic consciousness was considered a hypothetical psychological factor that could explain community resistance. In this study, it was introduced because transmission efficiency was found to vary over time, according to increases or decreases in reported patient numbers shown in previous research [13][27]. We hypothesised that media reports of increased cases would increase the level of pandemic consciousness, thus catalysing risk-evasive behaviours (e.g. not going out or wearing face masks and washing hands more frequently). Behavioural actions were parameterised as protective behaviour, then calibrated along the time course of real patient numbers; this effect was assumed to be reversible. The probability to engage in protective behaviour was set to 0.6 for the pandemic condition. This was derived on the basis of the results of a survey conducted by TDB-CAREE [28], which reported that about 60% of respondents believed more stringent measures were necessary in Tokyo as of June 2020. This subpopulation was therefore considered more likely to engage in protective behaviour. Meanwhile, new-normal lifestyle effects included the tendency to engage in remote work. This was handled as non-reversible based on the recognition that barriers to remote work included cyber security issues and employment rules.
As mentioned earlier, mass viral screening was not implemented in Japan, where virus testing was instead limited to symptomatic patients. During the early stages of the outbreak, typical symptoms were considered fever, fatigue, and/or shortness of breath. Our model was constructed in accordance with these conditions.
Integrating a quantitative systems model across disease transmission, people flow, and the restaurant industry
Our quantitative stock and flow model consisted of three components, including a disease transmission model, people flow and behaviour model, and effect on the restaurant industry model (Figure 4). First, the disease transmission model posited that virus carriers would transmit the virus to susceptible persons. We modelled symptomatic and non-symptomatic infections using data showing confirmed positive cases based on Japanese practices (i.e. virus testing was fundamentally limited to confirmative testing for symptomatic patients). Within the model, infections were considered dependent on the basic reproduction number [29], interpersonal contact, temperature [15], and the proportion of susceptible persons (i.e. non-immunised). On the other hand, we did not include virus mutations, possible vaccinations, or mass virus screening.
Second, the people flow and behaviour model posited that interpersonal contact related to disease transmission was affected by maximum people flow (i.e. locations for disease transmission) and personal behaviour (personal protective measures). Within the model, both elements were affected by psychological factors and short-term pandemic consciousness. Meanwhile, people flow was further dependent on extrinsic factors, such as stay-at-home requests and new-normal lifestyle effects, while behaviour was further affected by the distancing effect, behaviour guidance, and the thoroughness of protective behaviour.
Third, the restaurant industry model posited that customer visits to high-grade restaurants were dependent on the intention to dine out, but not necessarily dependent on people flow. As the interactions between customer visits and eWOM were unclear, they were modelled as independently affected by similar factors, such as stay-at-home requests, focused intervention effects, mid-term pandemic consciousness, long-term pandemic consciousness, and the psychological effect of school closures. Here, mid-term pandemic consciousness refers to a continuous mindset spanning months, particularly concerning the idea that individuals should voluntarily refrain from going out due to the risk of spreading disease. Next, long-term pandemic consciousness refers to a similar mindset that remains continuous for at least six months. This idea was introduced on the basis of the observation that customer visits and eWOM appeared to steadily react in contrast to fluctuating people flow. Finally, the psychological effect of school closures refers to both an initial recognition of the pandemic based on ministry-directed school closures [21][22] and a continued hypothetical psychological effect in which individuals avoid dining out as long as schools and other important educational facilities remain closed.
Though some part of the model structure was hypothetical, the quantitative aspects were calibrated based on real metrics, thus enabling useful simulations. In this regard, real conditions were investigated through real data, which were also used as a basis of comparison for the number of observed patients (confirmed positive viruses cases), people flow (obtained via smartphone location information), number of visits, and eWOM communication under realistic conditions.
NPI pattern simulation
We tested the effects of the four following interventional conditions: (A) realistic conditions, in which one stay-at-home request lasting 1.5 months was issued in April 2020 (first pandemic wave). However, countermeasures against the second wave were limited to appeals for protective behaviour and remote work; (B) hypothetical stay-at-home request lasting 1 month was issued in July 2020, specifically as a countermeasure against the second pandemic wave; (C) hypothetical stay-at-home request lasting 1 month was issued in June, specifically as a pre-emptive countermeasure against a second pandemic wave; (D) an exhaustive intervention scenario, in which a first stay-at-home request lasting 2 months was issued in March 2020, specifically as a pre-emptive countermeasure against a first pandemic wave, with a second stay-at-home request lasting 2 months being issued in July 2020.
The number of patients (evaluated as confirmed positives) differed between scenarios (Figure 5A), with stay-at-home requests (especially when pre-emptively issued) lowering the number of patients. On the other hand, the more exhaustive intervention with stay-at-home request tended to result in more negative economic effects (Figure 5B), as represented by reduced customer visits. The outcome that was based on the direct effect size of the stay-at-home request was parameterised as a 10% decrease in customer visits and eWOM communication. More specifically, this parameterisation was based on the consideration that stay-at-home requests without closures (as actually directed in January 2021) do not constitute strong interventions. For reference, a previous study found a small add-on effect related to the lockdown condition [1].
There were two important findings. First, scenario (B) (pre-emptive stay-at-home request to counteract the second pandemic wave) effectively controlled the pandemic in the short-term context, with only small negative impacts to restaurant businesses; however, prematurely lifting the request would cause an explosive growth in the number of infections. Second, based on the current effect size of the employed factors, the economic effects of an additional lockdown were small, but the anti-pandemic effects were large. These findings indicate that a mild lockdown of substantial duration is an effective way to curtail the effects of the virus.