COVID-19 is certainly one of the worst pandemics ever. As of 20 April 2020, the virus has generated over 2 million of confirmed infected cases and 150 thousand deaths [1] . In the absence of a vaccine, classical epidemiological measures such as testing in order to isolate the infected people, quarantine and social distancing are ways to reduce the growing speed of new infections as much as possible and as soon as possible. But, the economical harm of these measurements is estimated to be much more than that of the economical crisis of 2008 [2] . On the other hand, some studies [3] suggest that quarantine and social distancing measures might be needed for as long as 18 months, and will only be turned on and off alternatively during that period. In order to get a better understanding and make quick and optimal reactions to the current situation, many researchers have decided to exploit the various M&S tools and techniques [4] [5] [6] . In this paper, we aim to explain through M&S the current situation of the Covid 19 pandemic in Casablanca, Morocco, in order to reinforce the "so far" efficient measures, and also suggest a context tailored optimal strategy of release in order to contain and mitigate the spread of the virus while keeping the economy as near to normal as possible.
The urgency of the current situation and the fact that the targeted reader is meant to be from any background related to this subject is what guided the plan of this article to be as straight-forward, concise and practical as it can be. Therefore, section 2 is a brief presentation of the studied region (the city of Casablanca), its eight districts and some of their socio-economical characteristics. Section 3 discusses the current situation of Covid 19 in Casablanca. Section 4 is a walkthrough the simulations techniques used to explain the previously presented pandemic's situation. And finally in section 5 we suggest (what we believe to be) an optimal strategy for the after lockdown time as the Moroccan government is planning for a release in 20 May 2020.
Casablanca is the metropolitan economical capital of Morocco, most densely populated and currently, it holds the highest number of infections. Casablanca has eight districts (see figure 1 ), each district in Casablanca has its own demographic characteristics such as population size, density and dynamics but they don't differ that much. What might be the main difference between them is the type of each district (industrial, downtown, etc.)). But to summarize all briefly, there are three categories: 1 st category: Casa Anfa district serves as the city's economic and administrative center, cultural identifier, and historical birthplace. 2 nd category: The three districts Ain Sbaa, Ain Chock and Bernoussi are host to lots of industrial areas and businesses. Each category of districts maps into one of three classes, this classification is based on the number of transportations quantity and means provided for a certain district and also on the number of reasons people would go there, such as super market, work, hospitals, etc. which can be found in the official website of the administrative division of Casablanca One thing to mention, this is not because people from these two districts respected the lockdown measurements the most. In fact the number of reported violations of the measurements is the highest among those two districts more than others. So why this is the case! Given that all districts have quite similar demographics, everyone expect that the one that starts first should be at the top of the ranking list.
And here is the choropleth map version of the above Because the city's center receives the 3 infected from each other region, city's center is now with 3x7 = 27 infected. Being as dynamic as such places, the contact rate tend to be much higher, inducing a high infection rate per period. Now Casa Anfa should be shut down. Consequently, economy will decline, thus no budget to buy health equipments and eventually the mortality rate will get very high. And same logic goes for the work places, it just would be a little lower because not everyone works in the same place but instead the effect is distributed among all three districts.
Also, the contact rate is relatively low in the four popular districts of the third category. This is due to the fact that people that are living in these areas and have regular jobs, their job's place is most likely located either in the city's center or in the three districts with work areas. Therefore, a considerable number of people spend most of the daytime in other four districts and not in their districts, and only after 6PM that they return. And because of lockdown measures, after 6PM no one is allowed to stay out, thus, the coming back people goes right to their homes after spending the whole daytime in their work places.
While some research [9] argues that a young-workforce release would lead to substantial economic and societal benefits without enormous health costs to the country, others [10] suggest a community-based incremental approach to the easing of lockdowns, tailored to demographic and social stratifications of risk.
Here, we present a more flexible mix of the above propositions with slight changes and added tips in order to fit the context of a developing country like Morocco.
2) The lockdown-release strategy:
Unless, either the virus ran out of people to infect or a vaccine is available, no matter how much people respects social distancing measures, at the end, if only one person was infected and had not been identified, the wave of infections will start again. Many M&S driven studies [11] [12] [13] predict that any non careful release after lockdowns will result in a new wave of infections
As presented by the 2018 Nobel Prize laureate, economist Paul Romer [14] , testing and isolating everyone every short period of time (each week or even each day) is certainly the best straight-forward strategy to prevent the society from a new wave of infections. But given the fact that it's still a debate whether it is feasible or not in terms of the cost needed to make it in the United States, it is certainly not feasible to make it with that scale in a developing country such as Morocco. Thus, in the following, we present an adapted hybrid incremental strategy for lockdownrelease for the Moroccan-like countries.
In the majority of cases, these are areas where big companies, businesses and commercial centers are located, which means that they present a high contact rate. In addition, these areas are critical to the maintenance of the global economy, therefore identifying them can certainly be of huge benefit in mitigating the spread of the virus as well as maintaining the economy.
In our case, the area that presented the highest connection rate was Casa Anfa. This is because of the number of businesses, companies, government and private hospitals, high-quality education private schools, etc. This assumption was later verified by analyzing the transportation data in the official website of the administrative division of Casablanca Test, Isolate and trace within the identified areas: Until the Moroccan authorities have a sufficient amount of testing and isolation hotels capacity alongside with a contact tracing system for a targeted and non wasted test; not for the whole population; but only for people who live and/or work in the previously identified essential areas for the global economy, we believe that Morocco cannot reopen without having a new wave of infections as the most probable scenario.
Once we are pretty sure the identified areas are totally virusfree, we should not allow any visitors to come-in unless they are confirmedly tested negative for the maintenance of the public health of these areas, as well as the global economy.
Implementing this strategy in other metropolitan cities of the country an incremental manner is highly recommended since it will much more strengthen the global economy until it is near normal even with this infectious disease hanging around.
Another consideration might be to release the youth workers (20-30 years old) that are living apart from vulnerable people such as their parents, especially if they represent a significant proportion.
At this point in time, we shall begin releasing gradually people from the other areas while still keeping some of the essential good practices and measurements such as wearing masks and hand washing. Even if someone was tested positive now, we know for sure that this infected person did not go to the identified economical areas while he was infected (because we test anyone coming in).
In addition, even in the worst-case scenario, if an infected person transmitted the disease to lots of people, we now would have a good economy to assess the health system.
Surely, this strategy would require a big budget at the beginning for buying a large amount of testing kits (or making them locally), but let's think about it for a second, it is far much better to spend 1 Billion "for once", than to keep spending 400 Million each time for multiple lockdowns and releases loop.
In this paper, through a M&S driven analysis of the existing data of Casablanca city epidemic situation, we studied the main factors affecting the spread of COVID-19, leading us to determine three parameters as the most important ones: the number of infected people now, the contact rate and connection rate. What's more, is that our models helped us in inferring the reasons why some regions might be more susceptible for easy penetration and rapid spread of the virus than other regions. Not only that, but it also helped us to suggest what might be the optimal policy in order to contain and mitigate the spread of the virus while still maintaining the global economy as near to normal as possible. Finally, we hope that this article can make some contributions to the world's response in general and Moroccan's response in particular to this epidemic and give some references for future research. Future research will focus on applying the same approach described here for the prediction of the epidemic's evolution in other Moroccan and international regions (mainly cities) as well as adding other features related to optimal lockdown release strategies.
This manuscript reports an early version of the model and results, while deeper analysis is in progress.