Computers, Materials & Continua DOI:10.32604/cmc.2020.012314 

Article 
Analysis and Dynamics of Fractional Order Mathematical Model of COVID19 in Nigeria Using AtanganaBaleanu Operator
1Department of Mathematics, University of Ilorin, Ilorin, Kwara, Nigeria
2Department of Mathematics, AKI’s Poona College of Arts, Science and Commerce, Camp, Pune, India
3Department of Mathematics, College of Arts and Sciences, Prince Sattam bin Abdulaziz University, Wadi Aldawaser, Saudi Arabia
4Department of Mathematics, Cankaya University, Ankara, 06790, Turkey
5Institute of Space Sciences, MagureleBucharest, 077125, Romania
6Department of Medical Research, China Medical University Hospital, China Medical University, Taichung, 40447, Taiwan
7Faculty of Mathematics and Statistics, Ton Duc Thang University, Ho Chi Minh City, Vietnam
*Corresponding Author: Amjad S. Shaikh. Email: amjatshaikh@gmail.com
Received: 25 June 2020; Accepted: 30 August 2020
Abstract: We propose a mathematical model of the coronavirus disease 2019 (COVID19) to investigate the transmission and control mechanism of the disease in the community of Nigeria. Using stability theory of differential equations, the qualitative behavior of model is studied. The pandemic indicator represented by basic reproductive number R0 is obtained from the largest eigenvalue of the nextgeneration matrix. Local as well as global asymptotic stability conditions for the diseasefree and pandemic equilibrium are obtained which determines the conditions to stabilize the exponential spread of the disease. Further, we examined this model by using Atangana–Baleanu fractional derivative operator and existence criteria of solution for the operator is established. We consider the data of reported infection cases from April 1, 2020, till April 30, 2020, and parameterized the model. We have used one of the reliable and efficient method known as iterative Laplace transform to obtain numerical simulations. The impacts of various biological parameters on transmission dynamics of COVID19 is examined. These results are based on different values of the fractional parameter and serve as a control parameter to identify the significant strategies for the control of the disease. In the end, the obtained results are demonstrated graphically to justify our theoretical findings.
Keywords: Mathematical model; COVID19; AtanganaBaleanu fractional operator; existence of solutions; stability analysis; numerical simulation
The ongoing ravaging COVID19 is a contagious disease instigated by SARSCoV2. The first case of the disease was reported in December 2019 in Wuhan, China, and has, within few weeks, spread across the globe, leading to the present 2020 COVID19 pandemic [1]. The coronavirus disease 2019 has been regarded as the largest global health crisis in human history as a result of the magnitude of confirmed cases, accompanied by the degree of fatalities across the continents [2]. Reliable data had it that by April 2020, COVID19 pandemic had led to over 3 million confirmed cases with 230,000 deaths and the disease has spread to over 210 nations globally [3]. The symptoms and signs of COVID19 develop within 2 to 14 days [4]. When the disease is fully incubated, the infected individuals may exhibit fever, fatigue, cough and breathing disorder that is similar to those infections instigated by SARSCoV and MERSCoV [5]. However, many COVID19 acute cases and fatalities come from the elderly people (from the age of 65 upward) and individuals with severe health challenges (such as people with kidney disease, hypertension, diabetes, obesity and other health issues that deteriorate the immune system) [3].
The first confirmed case in Nigeria was reported on 27 February 2020, when a citizen from Italy is tested positive for the virus [6]. The disease transmission raised gradually over the month of April 2020, after a substantial number of cases were noted for in the country. Since then, Nigeria is focused on spotting and referring identified infectious patients for treatment to devoted COVID19 centers. As of 18 June 2020, Nigeria had reported 17,735 confirmed cases out of which 11,299 are active cases, 5,967 recovered peoples and 469 deaths due to COVID19 infection [7].
The global scourge of COVID19 pandemic has elicited the attention of scholars in different disciplines, prompting several proposals to examine and envisage the development of the pandemic [8]. Ndairov et al. [9] propose a model for the transmissibility of COVID19 in the presence of superspreaders individuals. They perform the stability and sensitivity analyses of the model and discovered that daily reduction in the number of confirmed cases of COVID19 is a function of the number of hospitalizations. Yang et al. [10] proposed a model to study the transmission pathways of COVID19 in terms of humantohuman and environmenttohuman spread. Their analysis confirms the tendency of COVID19 to remain pandemic even with prevention and intervention measures.
A model for the dynamics of COVID19 with parameter estimations, sensitivity analysis and data fitting is investigated in [11] while a model for COVID19 infection that describes the impact of slow diagnosis on the dynamics of COVID19 is also studied in [12]. In [13], the researchers employ a statistical study of coronavirus disease data to calculate timeregulated risk for fatality from the COVID19 in Wuhan. Their results indicate that movement restrictions and adequate social distancing procedures are capable of reducing the spread of the disease. Furthermore, a dataoriented model that includes behavioral impacts of humans and governmental efforts on the dynamics of COVID19 in Wuhan is proposed in [14]. A good number of mathematics and nonmathematics studies have also been conducted on COVID19 [15–21].
In recent times, the integer order differential systems are generalized and improved in order to formulate several mathematical models using fractional differential operators. Since, demonstration of some realworld phenomena with the help of fractional derivative operator is more appropriate and useful for improving performance of numerous engineering and applied sciences systems [22–29]. In this paper, initially we formulate the mathematical model in terms of integer order derivative and then apply the Atangana–Baleanu fractional derivative operator. The motivation behind utilizing the Atangana–Baleanu operator is that it has nonlocal and nonsingular kernel in the form of MittagLeffler function. Moreover, the complex behavior in the model must be ideal portrayed utilizing this operator. Literature pertaining to Atangana–Baleanu derivative and their applications to several systems arising in the field of applied sciences and engineering can be cited in [30–34].
The population of human under consideration is divided into six compartments which are susceptible S(t), since the incubation period of COVID19 is between two to fourteen days there are those who are infected without exhibiting any sign of symptoms and are undetected E(t). Individuals who are infected or suspected case of COVID19 need to go through an incubation period before the suspected symptom can noticeable these categories are quarantined Q(t), there are those certain proportion of the population have been infected with sign and symptoms of COVID19 and is highly infectious but not yet quarantined or isolated I(t). C(t) represent confirmed case of COVID19 from Quarantine category. R(t) represent recovery after treatment. The susceptible population is increased by immigration or by birth at the rate , in each of the class, individuals can die a natural death and the rate , there is a force of infection between the susceptible population and exposed population this is represented by , represent the progression from exposed class to highly infected class, the disease induced death rate for highly infected class, quarantine class and confirmed case of COVID19 class is represented by , proportion of people identified as suspected case of COVID19 are represented by , after medical diagnosis, some of the suspected cases were confirmed, others that are not detected can return back to the susceptible population at the rate . In the meantime, some highly infectious individuals will be moved to quarantine class at the rate . The progression rate from quarantine to confirm case after diagnosis is denoted by . The pictorial diagram illustrating the model is shown in Fig. 1 while the system of equations governing the model is given as:
The rest of the sections are organized as follows: Some valuable preliminaries dependent on the Atangana–Baleanu fractional operator is given in Section 3. In Section 4, we present stability analysis of the equilibria (drugfree equilibrium state and endemic equilibrium state). Analysis of fractional coronavirus model using the Atangana–Baleanu operator is given in Section 5. The Approximation technique and Numerical Simulation are given to reveal the behavior of dynamics components is accounted for in Section 6. The conclusion is finally drawn in the last Section 7.
This section of the paper will convert some basic definitions and properties related to Fractional calculus. During the paper process, we are going to refer to the following given specific definitions and properties of the Atangana–Baleanu fractional derivatives of Caputo type [32] that are peculiar to our study.
Definition 3.1 The Caputo fractional derivative for order is defined as
where
Definition 3.2 The Atangana–Baleanu fractional derivative for a given function for order in Caputo sense are defined as
where is a normalization function and is the MittagLeffler function.
Definition 3.3 Atangana–Baleanu fractional integral order is defined as
if is a constant, integral will be resulted with zero.
Definition 3.4 The Laplace transforms for the Atangana–Baleanu fractional operator of order where 0 is given as
Theorem 3.1. The following time fractional ordinary differential equation
has a unique solution considering the inverse Laplace transform and the convolution property below
4 Basic Properties of the Model
The invariant region sets out the domain where the model’s solutions are both biologically and mathematically meaningful. Since the model deals with human population, all of the model’s variables and parameters are assumed to be positive. To achieve this, we consider first the total human population Nh, where Nh = S + E + I + Q + C + R.
By differentiating with respect to t both side of the total population N
In the absence of the disease induced death due to COVID19 , Eq. (2) becomes
Integrating on both side
with the initial condition , where A is constant. Applying the initial condition in Eq. (4), we get
As in Eq. (5), the total human population reduces to . In this regard, all the feasible solution sets for human population in Eq. (1) enters and remains in the region
We therefore conclude that the proposed model is well posed and are both biologically and mathematically meaningful in the domain .
For the COVID19 model dynamics in Eq. (1) to be epidemiologically meaningful it is important to prove that all its state variables are positive for all time.
Theorem 4.1
Let the . Then the solutions are nonnegative for .
First, we consider the susceptible compartment in Eq. (1) give as
By applying the initial condition and solving the above Eq. (7), we get
By repeating the same procedure for respectively in the system Eq. (1), we obtained the following results
This shows that the solutions of the model are positive. Hence the proof.
4.3 DiseaseFree Equilibrium State (DFE)
The COVID19 model in Eq. (1) has a diseasefree equilibrium DFE obtain by setting the righthand side of Eq. (1) to zero. Therefore,
4.4 Existence of Endemic Equilibrium Point (EE)
We present the existence of the COVID19 endemic equilibrium states. It is a positive equilibrium state where the COVID19 disease is persisting in the population.
Theorem 4.2. Let there be a unique endemic equilibrium state when the basic reproduction number R0 > 1 in the COVID19 periodically forced model in Eq. (1).
Proof. Suppose is a nontrivial equilibrium state of system Eq. (1) which then connote that all the compartment of are nonnegative. By equating the lefthand side of Eq. (1) to zero we get the following endemic equilibrium states
where
4.5 Basic Reproduction Number R0
The basic reproductive ratio is a threshold quantity that represents the overall number of secondary diseases caused by a single infected individual created into a fully susceptible population throughout its infectious period. F and V are the matrices for the new infections generated and the terms of transition. Following the same approach as [35], we have
The Jacobian matrix of f and v computed at the diseasefree equilibrium is given as F and V such that
By substituting and from Eq. (11), we therefore obtain the basic reproduction number which is the spectral radius of the matrix as
4.6 Global Stability of the DiseaseFree Equilibrium
Theorem 4.3. If , then the diseasefree equilibrium is globally asymptotically stable otherwise it is unstable.
Proof. We consider the Lyapunov function of the type and
where,
From the result in Eq. (12), we can conclude that provided that. In addition, provided that or .
5 Analysis of Fractional Coronavirus Model Using the AtanganaBaleanu Operator
Let us consider the mathematical model given by an ordinary differential equation system Eq. (1) using Atangana–Baleanu fractional derivative operator as below
where represents the fractional operator of type Atangana–Baleanu–Caputo (ABC) having fractional order where 0 , subject to initial conditions
The system in Eq. (14) can be converted to the Volterratype integral equation by using the ABC fractional integral. The model is written by referring Theorem 3.1 as below:
Theorem 5.1 The kernels and given in Eq. (14) satisfy the Lipschitz condition and contraction if the following inequality holds:
Proof: Let the kernel
Let and be two functions; then we obtain the following:
where .
Similarly, we get,
where,
, and .
Considering the kernels of the model, Eq. (16) can be rewritten as
Therefore, we get the following recursive formula.
We next get the difference between the iterative terms in the expression
where
Applying the norm of both sides and considering triangular inequality, the Eq. (21) becomes
Since the kernels satisfy the Lipschitz condition, we get the following
This completes the proof of the theorem.
Theorem 5.2 (Existence of the Solution). The system given by Eq. (14) has a solution under the conditions that we can find satisfying
.
Proof: Let the functions S(t), E(t), I(t), Q(t), C(t) and R(t) are bounded. From Eq. (23) we get the following relations.
Hence, the functions and given in Eq. (24) exist and are smooth. Moreover, to show that the functions in Eq. (24) are the solutions of Eq. (14), we assume that
where and are reminder terms of series solution. Then, we must show that these terms approach to zero at infinity, that is,
,
and Thus, for the term
Continuing this way recursively, we get
where .
When we take the limit of both sides as n tends to infinity, we get
6 The Approximation Technique and Numerical Simulation
Consider the coronavirus model Eq. (14) along with initial conditions Eq. (15). The terms SI in this model is nonlinear. Implementing the Laplace transform on both sides of Eq. (14), we obtain,
Rearranging, we get
Further, the inverse Laplace transform on Eq. (29), yields
The series solutions achieved by the method are given by,
The nonlinearity of SI is written as whereas is further decomposed as follows [23]
Using initial conditions, we get the recursive formula given by
where
The approximate solution is assumed to obtain as a limit when n tends to infinity.
In this section, we have presented data fitting, numerical simulations and graphical demonstration of the Atangana Baleanu COVID19 model Eq. (14) for the population of Nigeria. We consider the available cumulative infection cases for April 1, 2020, till April 30, 2020 and parameterized the model [36]. The parameters were estimated based on the some assumptions and facts given in Tab. 1 which plays significant role in estimating R0 (basic reproductive number). R0 is expected number of cases directly generated by one individual in a population. When R0 > 1 the infection will be able to start spreading in a population, but if R0 < 1 the disease will die out.
Next, we evaluate and present the number of cumulative infectious cases in different compartments with respect to time in days using various plots for population of Nigeria. We begin estimation of our model from initial time (t = ) as per data reported on April 1, 2020 [6]. Hence, the required initial values are S(0) = ; E(0) = 15,000; I(0) = 100; Q(0) = 100; C(0) =175; R(0) = 31.
By applying iterative Laplace transform using Eq. (31) successively up to four terms we get series form approximate solution of the fractional COVID19 model Eq. (14) as given below
In Tab. 1, we have estimated some needed biological parameter values related with basic reproduction number corresponds to model (1) like, covid19 infection death rate (), force of infection (), proportion of people identified as suspected cases (), progression rate from exposed class to highly infected class () and other parameters are fitted from previous literature. Estimating these parameters to suitable values decreases rate of infection meaningfully. It is examined and noted that if is near to 2 the number of cumulative infected population rises very quickly. Also reducing the value of near to one lowers the number of infected cases rapidly.
Figs. 2a–7b shows the dynamical behaviour of various classes of mathematical model like susceptible population S(t), symptomatic and undetected population E(t), highly infectious but not yet quarantined or isolated I(t), individuals who are infected or suspected and quarantined Q(t), confirmed and quarantine population C(t), recovered population R(t) with = 1.96 and = 1.16 respectively for various values of = 1, 0.9, 0.8, 0.7 verses time in days. It is observed that as the value of decreases from the effect of the fractional derivative order becomes prominent. We clearly observe the significant variance in both type of plots (a) and (b) in each figure when value of fractional parameter changes. From Figs. 3a and 3b, it is noticed that as the time increase with respect to time the symptomatic and undetected population E(t) also increases due to spread of infection in the population and their interaction with infected people. It is clear that reducing the value of fractional parameter significantly affect COVID19 dynamics and greatly decrease the fraction of asymptomatic carriers with level of infection in the population. Hence, the number of cumulative cases of infections in every class is continuously depends upon the values of fractional order.
Also, Fig. 8a shows the comparison between estimated and actual number of cumulative cases of confirmed and quarantine population C(t) for data of available infection cases from April 1, 2020, till April 30, 2020 of Nigeria. This clearly shows that estimated and actual cases of infections are very near to each other. Fig. 8b shows the plots of total infected population in various compartments of model Eq. (1) versus time (days).
In this manuscript, we have analysed and examined transmission dynamics of COVID19 infection formulated in terms of mathematical model based on fractional differential system. We have used Atangana–Baleanu fractional derivative operator to obtain existence criteria of solution of mathematical model for the operator. The numerical simulations are carried out using iterative Laplace transform method. The essential axioms of the proposed model have been studied to observe the biological and mathematical feasibility. Further, we have examined the sensitivity analysis by finding the basic reproductive number which explains the significant of every biological parameter involved in the proposed model. Moreover, the local and global asymptotic stability conditions for the diseasefree and endemic equilibrium are obtained which determines the conditions to stabilize the exponential spread of the disease. It is noted from this analysis, that parameters and strengthen the outbreak of the infection at large extent and needs notable consideration to implement some control strategies to keep this under control. Towards the end all the hypothetical results are supported with the assistance of graphical portrayal by numerical investigation which would be beneficial for researchers to contemplate the dynamics of the COVID19.
Funding Statement: The authors received no specific funding for this study.
Conflicts of Interest: “The authors declare that they have no conflicts of interest to report regarding the present study.”
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