Ratio Mathematica Volume 43, 2022 Controlling Measles Transmission Dynamics with Optimal Control Analysis Chinwendu E. Madubueze* Isaac O. Onwubuya† Iorwuese Mzungwega‑ Abstract In this paper, a deterministic model for the transmission dynamics of measles infection with two doses of vaccination and isolation is studied. The disease-free equilibrium state and basic reproduction number, 𝑅0, of the model are computed. The sensitivity analysis of the model parameters is carried out using the Latin Hypercube Sampling (LHS) scheme in other to ascertain the parameters that contribute to the spread of measles in the population. The result of the sensitivity analysis shows that transmission rates, vaccination rates and isolation of the infected persons in the prodromal stage are significant parameters to be targeted for the eradication of measles infection. Based on the result of sensitivity analysis, an optimal control model with nutritional support as a control is developed. The analysis of optimal control model is carried out using Pontryagin’s maximum principle to identify the optimal control strategies to be adopted by public health practitioners and health policy makers in curtailing the spread of measles infection. The result of the optimal control analysis via numerical simulations revealed that combined timely implementation of correct administration of the two doses of vaccination, isolation of infected persons in the prodromal stage and mass distribution of nutritional support would curtail the measles disease outbreak in the population. However, in a situation where there is a limited facility to isolate the infected persons in * Chinwendu E. Madubueze (Joseph Sarwuan Tarka Univerisity, Makurdi, Nigeria); ce.madubueze@gmail.com. † Isaac O. Onwubuya (Joseph Sarwuan Tarka Univerisity, Makurdi, Nigeria); isaacobiajulu@gmail.com. ‑ Iorwuese Mzungwega (Joseph Sarwuan Tarka Univerisity, Makurdi, Nigeria). ‑ Received on April 17th, 2022. Accepted on August 12th, 2022. Published on September 25th, 2022. doi:10.23755/rm.v41i0.742. ISSN: 1592-7415. eISSN: 2282-8214. Β©The Authors. This paper is published under the CC-BY licence agreement. mailto:ce.madubueze@gmail.com mailto:isaacobiajulu@gmail.com C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega the prodromal stage, the combined implementation of mass distribution of nutritional support and administration of the two doses of vaccination will still eradicate measles infection in the population. Keywords: Measles; Nutritional Support; Vaccination; Isolation; Sensitivity Analysis; Pairwise Comparison; Optimal Control Analysis. 2010 AMS subject classification: 49K15, 49K40, 90C31, 34D20, 34C60. 1. Introduction Measles is a viral infectious disease caused by a single-stranded RNA virus that belongs to the group of Morbilliviruses of the Paramyxoviridae family. It is a seasonal disease that occurs mostly during the dry season in tropical zones where it is endemic and it peaks during late winter and early spring in temperate zones [24]. Non-immune people are infected via direct contact with the nasal and oral secretions or inhaling the aerosol droplets of an infected person. Ninety percentage of non-immune people are exposed to an infective and have the chance of being infected with measles disease [24, 27]. Measles has an average of 10 - 12 days incubation period. The incubation period is the interval from exposure to the prodromal stage [28], which spans for seven days of the infection period, after which the infective recovers with lifelong immunity against the disease. The symptoms of measles are based on different stages of the disease. Prodromal stage symptoms include high fever, runny nose (coryza), cough, and red eyes (conjunctivitis) that lasts 2 to 4 days with a range of 1- 7 days, while the rash stage symptoms occur a few days after the initial symptoms. The rash stage can lead to fatal complications or death if not treated early [10,12]. Annually, measles affects up to 20 million people worldwide and most cases are from Africa and Asia [24]. According to a report from World Health Organization and United State Center for Diseases Control and Prevention (CDC) [44, 45], 869,770 infection cases with 207,500 deaths of Measles were recorded globally in 2019, making it the highest number since the 1996 outbreak and has 50% increment as of 2016. For sub-Saharan Africa, about 134,200 measles deaths were recorded in 2015, while Nigeria recorded a significant increase of 28,400 cases in 2019 compared with 5,067 cases in 2018. Despite the cases dropping to 9,316 in 2020, the confirmed cases of measles remain high, and the case fatality is yet to be eased anytime there is an outbreak. This implies that comprehensive efforts and intervention strategies to reduce the menace of measles is crucial. Therefore, it is imperative to examine the optimal strategy that can be implemented to control measles disease in high-burden countries. According to WHO, the two major strategies to eradicate measles are vaccine and treatment [21, 23]. Isolation of infected people is also important in preventing further spread of the disease. However, increasing population immunity through vaccination remains the most effective way to prevent outbreaks of measles in a community [22]. The vaccination is mainly based on MMR (measles, mumps, and rubella) and MMRV (measles, mumps, rubella, and varicella) vaccines. These vaccines are about 95% effective as they globally prevent 4.5 million deaths yearly [16]. There are two doses of Controlling measles transmission dynamics with optimal control analysis MMR vaccine. The first dose produces 90% to 95% immunity to measles while the second dose produces a stronger immunity for those that do not respond to the first dose [17]. Among the childhood vaccine-preventable diseases, measles causes the most deaths in children. Measles outbreaks is prevented in a community if 90% to 95% of children are vaccinated. Mathematical models of infectious diseases are useful in studying transmission dynamics of diseases, testing theories, planning, implementing, evaluating and comparing various control programs that will prevent the further spread of diseases and their epidemics. A notable number of mathematical models have been elaborated and applied to infectious diseases like measles [4, 7, 9, 18, 25]. Some authors, like [8, 10, 19], developed an SEIR model of measles where testing and diagnosis therapy was incorporated as in [10] at the latent period. Authors [15, 20] considered the effect of supplemental immunization activities as an optimal policy for measles using an age- stratified compartmental model. Stephen et al. [17] revealed that the spread of measles disease largely depends on the contact rates with infected people within a population and the disease dies out in the population if the proportion of the population that is immune exceeds the herd immunity level. Vaccination is considered in the autonomous models [3, 4, 11, 13, 19, 29] as constant parameter or compartment for vaccinated people, while in [27-31], it is examined as a time-dependent control function to determine the optimal vaccination strategy that can be implemented to control measles in high-burden countries. Although [30 – 35] considered optimal control of vaccination for measles, the effect of two doses of vaccination and nutritional support are not studied. However, the authors [3, 37, 40] examined the effect of two doses of vaccination and isolation on measles disease as constant parameters without nutritional support impact and optimal control analysis. As advised by WHO [46], it is important to consider the effect of two doses of vaccination and nutritional support on measles transmission dynamics, which forms the study’s motivation. This involves modification of the model by [3] to investigate the impact of the two doses of vaccination, nutritional support and isolation on measles dynamics using sensitivity analysis and optimal control analysis approaches. This will help to provide the mathematical analysis of the possible control strategy (vaccine and nutritional support) that will help the public health practitioners to achieve the best strategy for the prevention and control of the spread of measles in community. The rest of the paper is organized as follows: Section 2 is the model formulation for measles with constant control measures. The model analysis is discussed in Section 3 which includes sensitivity analysis. We obtained the optimal control of the formulated model in Section 4. In Section 5, we carried out numerical simulation to verify some analytic results and their discussion, while Section 6 is the conclusion. 2. Model formulation A deterministic model for measles disease is presented by modifying the model by Aldila and Asrianti [3]. The total population at any time (𝑑) denoted by 𝑁(𝑑), is sub- divided into Susceptible persons, 𝑆(𝑑), Exposed persons, 𝐸(𝑑), Infected persons in prodromal stage, 𝑃(𝑑), Infected persons in rash stage, 𝐼(𝑑), Isolated persons, 𝐽(𝑑), 1st C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega dose of vaccinated persons, 𝑉1(𝑑), 2 nd dose of vaccinated persons, 𝑉2(𝑑), and Recovered persons, 𝑅(𝑑) such that 𝑁 = 𝑆 + 𝐸 + 𝑃 + 𝐼 + 𝐽 + 𝑉1 + 𝑉2 + 𝑅. (1) The susceptible persons,𝑆(𝑑), decreases when they come in contact with the infected persons at a force of infection, πœ†1 and become exposed person or by vaccination with 1 st dose vaccine at a rate, 1. The persons vaccinated with 1 st dose vaccine may be infected at a force of infection, πœ†2 since vaccine is not 100% efficacy. The force of infections, πœ†1 and πœ†2, are given by πœ†1 = 𝛽1(𝑃+𝑛1𝐼+𝑛2𝐽) 𝑁 πœ†2 = 𝛽2(𝑃+𝑛1𝐼+𝑛2𝐽) 𝑁 } (2) where 𝛽1 and 𝛽2 are the transmission rate for the susceptible and 1 st dose vaccinated persons respectively, 𝑛1 and 𝑛2 are the parameters that reduce the infectivity of the infected persons in the rash stage and isolated persons respectively. The 1st dose of vaccinated persons, 𝑉1(𝑑) receive 2 nd dose vaccine at a rate, 2 and achieve immunity at the rate, 𝜎. The exposed persons, 𝐸(𝑑), becomes infected persons in the prodromal stage, 𝑃(𝑑) at a rate, π‘˜ after incubation period of measles disease. The infected persons in the prodromal stage, 𝑃(𝑑), then progress to rash stage at a rate, 𝛼 while some are isolated for further treatment at a rate, πœ‘1 or they recovered at a rate, 𝛿1. In a similar way, the infected persons at the rash stage, 𝐼(𝑑), are isolated at a rate, πœ‘2 or recovered from measles at a rate, 𝛿2. Meanwhile, the isolated persons recovered at a rate, 𝛿3. It is assumed that all the subpopulations experience natural death at a rate, πœ‡ and the subpopulations, 𝐼(𝑑) and 𝐽(𝑑) may die of measles disease at 𝑑1 and 𝑑2 respectively. The model description and details of the model parameters are presented in Figure 1 and Table 1. respectively. With Figure 1 and Table 1, the transition within subpopulations are expressed by the following system of first order differential equations; Controlling measles transmission dynamics with optimal control analysis 𝑑𝑆 𝑑𝑑 = Ξ› βˆ’ πœ†1𝑆 βˆ’ ( 1 + πœ‡)𝑆, 𝑑𝑉1 𝑑𝑑 = 1𝑆 βˆ’ (πœ†2 + 2 + πœ‡)𝑉1, 𝑑𝑉2 𝑑𝑑 = 2𝑉1 βˆ’ (πœ‡ + 𝜎)𝑉2, 𝑑𝐸 𝑑𝑑 = πœ†1𝑆 + πœ†2𝑉1 βˆ’ (πœ‡ + π‘˜)𝐸, 𝑑𝑃 𝑑𝑑 = π‘˜πΈ βˆ’ (𝛼 + πœ‡ + πœ‘1 + 𝛿1)𝑃, 𝑑𝐼 𝑑𝑑 = 𝛼𝑃 βˆ’ (πœ‘2 + 𝛿2 + πœ‡ + 𝑑1)𝐼, 𝑑𝐽 𝑑𝑑 = πœ‘1𝑃 + πœ‘2𝐼 βˆ’ (𝛿3 + πœ‡ + 𝑑2)𝐽, 𝑑𝑅 𝑑𝑑 = πœŽπ‘‰2 + 𝛿1𝑃 + 𝛿2𝐼 + 𝛿3𝐽 βˆ’ πœ‡π‘…} (3) where πœ†1 = 𝛽1(𝑃+𝑛1𝐼+𝑛2𝐽) 𝑁 , πœ†2 = 𝛽2(𝑃+𝑛1𝐼+𝑛2𝐽) 𝑁 and the initial conditions, 𝑆(0) > 0,𝑉1(0) β‰₯ 0,𝑉2(0) β‰₯ 0,𝐸(0) β‰₯ 0,𝑃(0) β‰₯ 0,𝐼(0) β‰₯ 0,𝐽(0) β‰₯ 0, 𝑅(0) β‰₯ 0. The model parameters are assumed to be nonnegative except recruitment rate, Ξ›, that is strictly positive. Figure 1. Model flow diagram for transmission dynamics of measles disease. C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega Table 1. Parameters and their descriptions Parameters Parameters Description (Ranges)Nominal values Sources 𝚲 𝜷𝟏 𝜷𝟐 𝜺𝟏 𝜺𝟐 π’πŸ π’πŸ 𝝁 π’Œ 𝜢 𝜹𝟏 𝜹𝟐 πœΉπŸ‘ π’…πŸ π’…πŸ 𝝎𝟏 𝝎𝟐 𝝈 Recruitment rate Transmission rate for 𝑆(𝑑) class Transmission rate for 𝑉(𝑑) class Vaccination rate of first dose vaccine Vaccination rate of second dose vaccine Infectivity reduction rate for 𝐼(𝑑) class Infectivity reduction rate for 𝐽(𝑑) class Natural death rate Progression rate from 𝐸(𝑑) to 𝑃(𝑑) Progression rate from 𝑃(𝑑) to 𝐼(𝑑) Recovery rate for 𝑃(𝑑) class Recovery rate for 𝐼(𝑑)class Recovery rate for 𝐽(𝑑) class Disease-related death rate for 𝐼(𝑑)class Disease-related death rate for 𝐽(𝑑) class Isolation rate for 𝑃(𝑑) class Isolation rate for 𝐼(𝑑) class Immunity rate due to 2nd dose of vaccine (βˆ’)2000 (0.0004 βˆ’ 0.5)0.6 (0.0003 βˆ’ 0.4)0.5 (0.01 βˆ’ 0.95)0.6 (0.01 βˆ’ 0.95)0.01 (βˆ’)0.1 (βˆ’)0.01 (βˆ’)1 65.365⁄ (βˆ’)0.09 (βˆ’)0.003 (βˆ’)0.2 (βˆ’)0.06 (βˆ’)0.3121 (βˆ’)0.125 (βˆ’)0.1 (0.0001 βˆ’ 0.05)0.01 (0.001 βˆ’ 0.5)0.001 (βˆ’)0.01 [1] Assumed Assumed [38] Assumed [3] [3] [3] [1] Assumed [3] Assumed [36] [39] [1] [1] Assumed [38] 3. Model analysis Here, the well-poseness of system (3) is established which implies that the model makes biological sense. This is done by proving the existence of nonnegative solutions and boundedness of the model (3) when given initial solutions of the model. Theorem 1. With the initial solutions, 𝑆(0) > 0, 𝑉1(0) β‰₯ 0, 𝑉2(0) β‰₯ 0, 𝐸(0) β‰₯ 0, 𝑃(0) β‰₯ 0, 𝐼(0) β‰₯ 0, 𝐽(0) β‰₯ 0,𝑅(0) β‰₯ 0, the model equation (3) has non-negative solutions for all time, 𝑑 > 0. Proof. Let 𝑑1 = 𝑠𝑒𝑝{𝑑 > 0: 𝑆(0) > 0, 𝑉1(0) β‰₯ 0, 𝑉2(0) β‰₯ 0, 𝐸(0) β‰₯ 0, 𝑃(0) β‰₯ 0, 𝐼(0) β‰₯ 0, 𝐽(0) β‰₯ 0,𝑅(0) β‰₯ 0} ∈ [0,𝑑]. Controlling measles transmission dynamics with optimal control analysis From the first equation of system (3), we have 𝑑𝑆 𝑑𝑑 = Ξ› βˆ’ πœ†1𝑆 βˆ’ 1𝑆 βˆ’ πœ‡π‘† β‰₯ βˆ’( 1 + πœ‡ + πœ†1)𝑆. Applying the method of integrating factor with initial condition, 𝑆(0), we have 𝑆(𝑑) β‰₯ 𝑆(0)exp {βˆ’βˆ« ( 1 + πœ‡ + πœ†1) 𝑑 0 𝑑1} > 0 which is always positive for 𝑑 > 0. In similar way, 𝑉1(𝑑) > 0,𝑉2(𝑑) > 0,𝐸(𝑑) > 0, 𝑃(𝑑) > 0, 𝐼(𝑑) > 0, 𝐽(𝑑) > 0, 𝑅(𝑑) > 0 for 𝑑 > 0. This means that the solution set 𝑆(𝑑),𝑉1(𝑑),𝑉2(𝑑),𝐸(𝑑),𝑃(𝑑),𝐼(𝑑),𝐽(𝑑),𝑅(𝑑) of the system (3) is non-negative for all 𝑑 > 0. To show the boundedness of the solutions of the system (3), we state and prove feasible region of the system (3). Theorem 2. The solutions of system (3) are contained in the feasible region, Ξ© = {(𝑆, 𝑉1,𝑉2,𝐸,𝑃,𝐼, 𝐽,𝑅) ∈ β„œ+ 8 : 𝑁 ≀ Ξ› πœ‡ } with the non-negative initial conditions. Proof. To obtain the total population, 𝑁(𝑑), we sum up the equations of system (3) to yields 𝑑𝑁 𝑑𝑑 = Ξ› βˆ’ πœ‡π‘ βˆ’ 𝑑1𝐼 βˆ’ 𝑑2𝐽 ≀ Ξ› βˆ’ πœ‡π‘. (4) Applying Gronwall’s inequality with the initial condition, 𝑁(0) = 𝑁0 in equation (4) gives 𝑁(𝑑) ≀ Ξ› πœ‡ + [𝑁0 βˆ’ Ξ› πœ‡ ]π‘’βˆ’πœ‡π‘‘. (5) If 𝑁0 > (<) Ξ› πœ‡ , the total population, 𝑁, tends to Ξ› πœ‡ as 𝑑 β†’ ∞. Thus, in either case, the total population, 𝑁(𝑑) β†’ Ξ› πœ‡ as 𝑑 β†’ ∞ in (5). Hence, the solution set of system (3) will enter the feasible region, Ξ© that is positively invariant. 3.1 Existence of disease-free equilibrium state and basic reproduction number Disease-free equilibrium state occurs when there is no infection in the population, that is when the infected state variables are zero. Solving simultaneously at equilibrium state, 𝑑𝑆 𝑑𝑑 = 0, 𝑑𝑉1 𝑑𝑑 = 0, 𝑑𝑉2 𝑑𝑑 = 0, 𝑑𝐸 𝑑𝑑 = 0, 𝑑𝑃 𝑑𝑑 = 0, 𝑑𝐼 𝑑𝑑 = 0, 𝑑𝐽 𝑑𝑑 = 0, 𝑑𝑅 𝑑𝑑 = 0 of the system (3) gives the disease-free equilibrium state, C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega 𝐸0 = (𝑆 0,𝑉1 0,𝑉2 0,𝐸0,𝑃0, 𝐼0, 𝐽0,𝑅0) = ( Ξ› (πœ€1+πœ‡) , πœ€1Ξ› 𝑓(πœ€1+πœ‡) , πœ€1πœ€2Ξ› 𝑓(𝜎+πœ‡)(πœ€1+πœ‡) ,0,0,0,0, πœŽπœ€1πœ€2Ξ› πœ‡π‘“(𝜎+πœ‡)(πœ€1+πœ‡) ) (6) with 𝑓 = 2 + πœ‡. Basic Reproduction Number, 𝑅0 The basic reproduction number is a threshold quantity that determines the persistence and eradication of the infectious disease in the population, making it the most important quantity in infectious disease epidemiology. It is defined as the mean number of persons infected when a single infective is introduced into a wholly susceptible population [6]. 𝑅0 is computed using the next-generation matrix approach [6]. Following the approach in [6], the rate of new infection, ℱ𝑖, and the rate of transitional terms, 𝒱𝑖, in compartment 𝑖, of the system (3) are given as ℱ𝑖 = ( 𝛽1(𝑃+𝑛1𝐼+𝑛2𝐽)𝑆 𝑁 + 𝛽2(𝑃+𝑛1𝐼+𝑛2𝐽)𝑉1 𝑁 0 0 0 ) , 𝒱𝑖 = ( 𝑔𝐸 βˆ’π‘˜Β£ + β„Žπ‘ƒ βˆ’π›Όπ‘ƒ + 𝑝𝐼 βˆ’πœ‘1𝐼 βˆ’ πœ‘2𝑃 + π‘žπ½ ), where 𝑖 = 1,…,4 is the number of infected compartments and 𝑔 = (πœ‡ + π‘˜),β„Ž = (𝛼 + πœ‘1 + 𝛿1 + πœ‡),𝑝 = (πœ‘2 + 𝛿2 + πœ‡ + 𝑑1),π‘ž = (𝛿3 + πœ‡ + 𝑑2). (7) Taking the partial derivative of ℱ𝑖 and 𝒱𝑖 with respect to 𝐸,𝑃,𝐼 π‘Žπ‘›π‘‘ 𝐽 at DFE, 𝐸0, we have respective Jacobian matrices 𝐹 = ( 0 (𝛽1𝑆 0+𝛽2𝑉1 0) 𝑁0 𝑛1(𝛽1𝑆 0+𝛽2𝑉1 0) 𝑁0 𝑛2(𝛽1𝑆 0+𝛽2𝑉1 0) 𝑁0 0 0 0 0 0 0 0 0 0 0 0 0 ) , 𝑉 = ( 𝑔 0 0 0 βˆ’π‘˜ β„Ž 0 0 0 βˆ’π›Ό 𝑝 0 0 βˆ’πœ‘1 βˆ’πœ‘2 π‘ž ), where 𝑁0 = 𝑆0 + 𝑉1 0 + 𝑉2 0 + 𝐸0 + 𝑃0 + 𝐼0 + 𝐽0 + 𝑅0 = Ξ› πœ‡ . Controlling measles transmission dynamics with optimal control analysis The inverse of 𝑉 is given as π‘‰βˆ’1 = ( 1 𝑔 0 0 0 π‘˜ π‘”β„Ž 1 β„Ž 0 0 π›Όπ‘˜ π‘”β„Žπ‘ 𝛼 β„Žπ‘ 1 𝑝 0 π‘˜(π›Όπœ‘2+π‘πœ‘1) π‘”β„Žπ‘π‘ž (π›Όπœ‘2+π‘πœ‘1) β„Žπ‘π‘ž πœ‘2 π‘π‘ž 1 π‘ž) . With definition of basic reproduction number, 𝑅0, as the spectral radius of matrix, πΉπ‘‰βˆ’1, we have 𝑅0 = (𝛽1𝑆 0+𝛽2𝑉1 0) 𝑁0 [ π‘˜ π‘”β„Ž + π›Όπ‘˜π‘›1 π‘”β„Žπ‘ + π‘˜π‘›2(π›Όπœ‘2+π‘πœ‘1) π‘”β„Žπ‘π‘ž ]. Upon substitution of 𝑆0 = Ξ› πœ€1+πœ‡ , 𝑉1 0 = πœ€1Ξ› 𝑓(πœ€1+πœ‡) and 𝑁0 = Ξ› πœ‡ , we have 𝑅0 = πœ‡(𝛽1𝑓+𝛽2πœ€1) 𝑓(πœ€1+πœ‡) [ π‘˜ π‘”β„Ž + π›Όπ‘˜π‘›1 π‘”β„Žπ‘ + π‘˜π‘›2(π›Όπœ‘2+π‘πœ‘1) π‘”β„Žπ‘π‘ž ]. By the virtue of next-generation matrix approach [6], the disease-free equilibrium, 𝐸0, of system (3) is locally asymptotically stable if 𝑅0 < 1 and unstable if 𝑅0 > 1. This means that the measles infection will die out in the population if 𝑅0 < 1 while it will persist in the population when 𝑅0 > 1. 3.2 Sensitivity analysis Sensitivity analysis plays an important role in examining the effect, influence and contribution of the parameters of a mathematical model to the model output. To know the type of intervention strategies to adopt in reducing the transmission and prevalence of any infectious disease, sensitivity analysis is carried-out to determine the biological significance of the model parameters in relation to the reproduction number, 𝑅0. We adopt the Latin Hypercube Sampling (LHS) scheme used by [41,42,43] with the Partial Rank Correlation Coefficients (PRCCs) procedure to assess the biological implications of each input parameter to the output parameter, the disease threshold, 𝑅0. This type of sensitivity analysis approach provides numerical results that enable us to explore the entire parameter space simultaneously, thereby producing an unbiased selection of the parameter values. The signs (positive or negative) of the PRCCs indicate the precise strength of the relationship between the input variables (parameters of the model) and the output variable, 𝑅0 in this case. It also provides an insight to the degree of monotonicity between the parameters of the model and 𝑅0. Thus, comparing the values of PRCCs enabled us to directly evaluate the impact of the model parameters on 𝑅0. C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega Figure 2 shows the PRCCs for some important parameters of the model. The parameters 𝛽1 and 𝛽2 have positive PRCCs meaning increasing their values increase 𝑅0, which in return increase the spread of measles infection in the population. Whereas, the parameters 1 , 2,πœ”1 and πœ”2 with negative PRCCs reduce the value of 𝑅0 when they are increased. They have the capacity of ameliorate the spread of measles infection in the population, which leads to the eradication of the disease in the population. However, the parameter πœ”2 has a small magnitude of PRCC that is non-monotonically related to 𝑅0 but it can still produce a change in the transmission dynamics of measles infection. In other to identify the model parameters that are significant in curtailing or enhancing the spread of measles disease, the Fisher Transformation is applied to the PRCCs to compute the p- values of each of the model parameters as used in [42]. This is shown in Table 2. It is observed in Table 2 that the parameters (𝛽1,𝛽2, 1 , 2,πœ”1) have p-values that are significant while the parameter, πœ”2, has an insignificance p-value. This is further shown in Figure 3 as scatterplots for 𝑅0 against some model parameters. From Figure 3, it is observed that the parameters (𝛽1,𝛽2, 1 , 2,πœ”1) have a significant impact on 𝑅0 than πœ”2. Figure 2. Tornados plot for some significant model parameters. Controlling measles transmission dynamics with optimal control analysis Figure 3. Monte Carlo simulations for some important parameters of the model generated using the parameter values in Table 1. In each simulation run, 1000 randomly selected parameters are used. Table 2. Parameter PRCC significance (unadjusted p-value) 0 0.5 1 -6 -4 -2 0 2  1 lo g (R 0 ) 0 0.5 1 -6 -4 -2 0 2  2 lo g (R 0 )0 0 0.5 1 -6 -4 -2 0 2 ο₯ 1 lo g (R 0 ) 0 0.5 1 -6 -4 -2 0 2 ο₯ 2 lo g (R 0 ) 0 0.05 0.1 -6 -4 -2 0 2  1 lo g (R 0 ) 0 0.005 0.01 -6 -4 -2 0 2  2 lo g (R 0 ) Parameter PRCC p-value Keep 𝜷𝟏 0.65564141 0.0000 TRUE 𝜷𝟐 0.57787305 0.0000 TRUE 𝜺𝟏 βˆ’0.67496222 0.0000 TRUE 𝜺𝟐 βˆ’0.65937154 0.0000 TRUE 𝝎𝟏 βˆ’0.54171573 0.0000 TRUE 𝝎𝟐 βˆ’0.01142558 0.7049 FALSE C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega Table 3. Pairwise PRCC Comparisons (unadjusted p-values) 𝜷𝟏 𝜷𝟐 𝜺𝟏 𝜺𝟐 𝝎𝟏 𝜷𝟏 0.00506 0 0 0 𝜷𝟐 0 0 0 𝜺𝟏 0.5314 2.048 Γ— 10 βˆ’6 𝜺𝟐 3.743 Γ— 10 βˆ’5 𝝎𝟏 Table 4. Pairwise PRCC Comparisons (FDR Adjusted p-values) 𝜷𝟏 𝜷𝟐 𝜺𝟏 𝜺𝟐 𝝎𝟏 𝜷𝟏 0.005622 0 0 0 𝜷𝟐 0 0 0 𝜺𝟏 0.5314 2.926 Γ— 10 βˆ’6 𝜺𝟐 4.679 Γ— 10 βˆ’5 𝝎𝟏 Table 5. Parameters different after FDR adjustment? 𝜷𝟏 𝜷𝟐 𝜺𝟏 𝜺𝟐 𝝎𝟏 𝜷𝟏 TRUE TRUE TRUE TRUE 𝜷𝟐 TRUE TRUE TRUE 𝜺𝟏 FASLE TRUE 𝜺𝟐 TRUE 𝝎𝟏 Tables 3 and 4 show the pairwise comparison of the important parameters of the model, whose p-values are less than 0.05.π‘‡β„Žπ‘–π‘  𝑖𝑠 to establish if there exist any difference between the processes describing the compared parameters. The results of the pairwise PRCC comparison for the unadjusted p-values and the false discovery rate (FDR) adjusted p-values are presented in Table 3 and Table 4, respectively. With the FDR adjusted p-values in Table 4, we present the parameters different in Table 5. If the p- values of the compared pair of significant parameters are less than 0.05, we say that they Controlling measles transmission dynamics with optimal control analysis are different (TRUE); otherwise not different (FALSE). We also noted from Table 5, that apart from 1 βˆ’ 2 pair, all other pairs of parameters are significantly different. Thus, the parameters 𝛽1,𝛽2, 1, 2, πœ”1 play a vital role in the eradication of the measles disease. Hence, the spread of measles infection will reduce drastically if the value of 𝑅0 is less than a unity (𝑅0 < 1), which implies reducing the values of 𝛽1 and 𝛽2 as well as increasing the values of 1, 2, πœ”1 . This establishes that isolating the infected individuals in the prodromal stage and minimizing contact with infected persons (both at the prodromal and rash stage) will eradicate the spread of measles in the population. Also, increasing the rate of correct administration of vaccines (first and second dose) will go a long way in reducing the number of infected individuals as many susceptible people will be protected by vaccination thereby minimize the spread of measles before and during the epidemic. 4. Optimal control analysis Optimal control has been extensively applied as a strategy in controlling many epidemic outbreaks. The main idea of applying the optimal control to disease epidemics is to choose among the available strategies, the most suitable and effective strategies that will reduce disease infection rate to a minimum level while optimizing the cost of deploying these strategies [26]. In terms of measles epidemics, such strategy can include therapies, vaccines, isolation and educational campaigns [5]. Based on the result of the sensitivity analysis, the functions, 𝑒1(𝑑),𝑒2(𝑑),𝑒3(𝑑),𝑒4(𝑑), are considered as time-dependent control functions where 𝑒1(𝑑) is mass distribution of nutrition (supplement) support that reduces the transmission rates, 𝑒2(𝑑) is the first dose vaccination control, 𝑒3(𝑑) is the second dose vaccination control and 𝑒4(𝑑) is the isolation of infected people in the prodromal stage. The nutritional support is to boost the immune system of the body. Thus, the optimal control model of the system (3) is given by 𝑑𝑆 𝑑𝑑 = Ξ› βˆ’ (1βˆ’π‘’1(𝑑))𝛽1(𝑃+𝑛1𝐼+𝑛2𝐽)𝑆 𝑁 βˆ’ 1𝑒2(𝑑)𝑆 βˆ’ πœ‡π‘†, 𝑑𝑉1 𝑑𝑑 = 1𝑒2(𝑑)𝑆 βˆ’ (1βˆ’π‘’1(𝑑))(1βˆ’π‘’2(𝑑))𝛽2(𝑃+𝑛1𝐼+𝑛2𝐽)𝑉1 𝑁 βˆ’ 2𝑒3(𝑑)𝑉1 βˆ’ πœ‡π‘‰1, 𝑑𝑉2 𝑑𝑑 = 2𝑒3(𝑑)𝑉1 βˆ’ (πœ‡ + 𝜎)𝑉2, 𝑑𝐸 𝑑𝑑 = (1βˆ’π‘’1(𝑑))𝛽1(𝑃+𝑛1𝐼+𝑛2𝐽)𝑆 𝑁 + (1βˆ’π‘’1(𝑑))(1βˆ’π‘’2(𝑑))𝛽2(𝑃+𝑛1𝐼+𝑛2𝐽)𝑉1 𝑁 βˆ’ (πœ‡ + π‘˜)𝐸, 𝑑𝑃 𝑑𝑑 = π‘˜πΈ βˆ’ (𝛼 + πœ‡ + πœ‘1 + 𝑒4(𝑑) + 𝛿1)𝑃, 𝑑𝐼 𝑑𝑑 = 𝛼𝑃 βˆ’ (πœ‘2 + 𝛿2 + πœ‡ + 𝑑1)𝐼, 𝑑𝐽 𝑑𝑑 = πœ‘1𝑃 + 𝑒4(𝑑)𝑃 + πœ‘2𝐼 βˆ’ (𝛿3 + πœ‡ + 𝑑2)𝐽, 𝑑𝑅 𝑑𝑑 = πœŽπ‘‰2 + 𝛿2𝐼 + 𝛿1𝑃 + 𝛿3𝐽 βˆ’ πœ‡π‘…. } (8) C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega These control functions are bounded, Lebesgue integrable functions that satisfy 0 ≀ 𝑒1 ≀ 1, 0 ≀ 𝑒2 ≀ 0.95, 0 ≀ 𝑒3 ≀ 0.95 and 0 ≀ 𝑒4 ≀ 1 with assumption that the highest vaccination coverage will be 95%. The goal is to reduce the number of infected people (𝑃(𝑑),𝐼(𝑑),𝐽(𝑑)) and increase the number of susceptible people 𝑆(𝑑) while minimizing the cost of implementing controls. Therefore, the objective function is given as Ξ“(𝑒1 ,𝑒2 ,𝑒3 ,𝑒4 ) = ∫ (𝑏𝑃 + 𝑐𝐼 + 𝑑𝐽 + 1 2 βˆ‘ π‘šπ‘–π‘’π‘– 2(𝑑)4𝑖=1 ) 𝑑𝑓 0 𝑑𝑑 (9) and is subject to equation (8) with the initial conditions of the system (3). In equation (9), the constants, 𝑏,𝑐,𝑑,π‘š1,π‘š2,π‘š3,π‘š4, are positive weights to balance the size of the terms attached with them and 𝑑𝑓 is the final time to implement the controls, 𝑒1(𝑑),𝑒2(𝑑),𝑒3(𝑑),𝑒4(𝑑). The terms, 𝑏𝑃,𝑐𝐼,𝑑𝐽 are the cost related to reducing the number of infected people (𝑃,𝐼,𝐽) such as cost of the mass distribution of nutrition (supplement) support, isolation and first dose and second dose vaccination at the due time. We seek optimal controls 𝑒1 βˆ—,𝑒2 βˆ—,𝑒3 βˆ—,𝑒4 βˆ— such that Ξ“(𝑒1 βˆ—,𝑒2 βˆ—,𝑒3 βˆ—,𝑒4 βˆ—) = π‘šπ‘–π‘›{Ξ“(𝑒1 ,𝑒2 ,𝑒3 ,𝑒4 )|𝑒1 ,𝑒2 ,𝑒3 ,𝑒4 ∈ π‘ˆ}. (10) With the application of Pontryagin’s maximum principle [14], the equations (8) and (9) are converted into a problem of minimizing pointwise a Hamiltonian, 𝐻 with respect to 𝑒1 ,𝑒2 ,𝑒3 ,𝑒4 . This is given by 𝐻 = 𝑏𝑃 + 𝑐𝐼 + 𝑒𝐽 + π‘š1𝑒1 2(𝑑) 2 + π‘š2𝑒2 2(𝑑) 2 + π‘š3𝑒3 2(𝑑) 2 + π‘š4𝑒4 2(𝑑) 2 + 1 (Ξ› βˆ’ (1 βˆ’ 𝑒1(𝑑))𝛽1(𝑃 + 𝑛1𝐼 + 𝑛2𝐽)𝑆 𝑁 βˆ’ 1𝑒2(𝑑)𝑆 βˆ’ πœ‡π‘†) + 2 ( 1𝑒2(𝑑)𝑆 βˆ’ (1 βˆ’ 𝑒1(𝑑))(1 βˆ’ 𝑒2(𝑑))𝛽2(𝑃 + 𝑛1𝐼 + 𝑛2𝐽)𝑉1 𝑁 βˆ’ 2𝑒3(𝑑)𝑉1 βˆ’ πœ‡π‘‰1) + 3( 2𝑒3(𝑑)𝑉1 βˆ’ (πœ‡ + 𝜎)𝑉2) + 4 ( (1 βˆ’ 𝑒1(𝑑))𝛽1(𝑃 + 𝑛1𝐼 + 𝑛2𝐽)𝑆 𝑁 + (1 βˆ’ 𝑒1(𝑑))(1 βˆ’ 𝑒2(𝑑))𝛽2(𝑃 + 𝑛1𝐼 + 𝑛2𝐽)𝑉1 𝑁 βˆ’ (πœ‡ + π‘˜)𝐸) + 5 (π‘˜πΈ βˆ’ (𝛼 + πœ‡ + πœ‘1 + 𝑒4(𝑑) + 𝛿1)𝑃) + 6 (𝛼𝑃 βˆ’ (πœ‘2 + 𝛿2 + πœ‡ + 𝑑1)𝐼) + 7 (πœ‘1𝑃 + 𝑒4(𝑑)𝑃 + πœ‘2𝐼 βˆ’ (𝛿3 + πœ‡ + 𝑑2)𝐽) + 8( πœŽπ‘‰2 + 𝛿2𝐼 + 𝛿1𝑃 + 𝛿3𝐽 βˆ’ πœ‡π‘…) Controlling measles transmission dynamics with optimal control analysis with 1, 2, 3, 4, 5, 6, 7, 8 as respective adjoint variables for the state variables, 𝑆,𝑉1,𝑉2,𝐸,𝑃,𝐼,𝐽,𝑅. The system of adjoint variables are derived by taking the partial derivative of 𝐻 with respect to each of their corresponding state variables. This is given by π‘‘πœ1 𝑑𝑑 = βˆ’ πœ•π» πœ•π‘† = π‘Ž + 𝐴(1 βˆ’ 𝑆 𝑁 )( 1 βˆ’ 4) + 𝐡𝑉1( 4 βˆ’ 2) + 1πœ‡ + 1𝑒2(𝑑)( 1 βˆ’ 2), π‘‘πœ2 𝑑𝑑 = βˆ’ πœ•π» πœ•π‘‰1 = 𝐡𝑁(1 βˆ’ 𝑆 𝑁 )( 2 βˆ’ 4) + 𝐴𝑆 𝑁 ( 4 βˆ’ 1)+ 2πœ‡ + 2𝑒3(𝑑)( 2 βˆ’ 3), π‘‘πœ3 𝑑𝑑 = βˆ’ πœ•π» πœ•π‘‰2 = 𝐡𝑉1( 4 βˆ’ 2)+ 𝐴𝑆 𝑁 ( 4 βˆ’ 1) + 𝜎( 3 βˆ’ 8) + 3πœ‡, π‘‘πœ4 𝑑𝑑 = βˆ’ πœ•π» πœ•πΈ = 𝐡𝑉1( 4 βˆ’ 2) + 𝐴𝑆 𝑁 ( 4 βˆ’ 1)+ ( 4 βˆ’ 5)π‘˜ + 4πœ‡, π‘‘πœ5 𝑑𝑑 = βˆ’ πœ•π» πœ•π‘ƒ = βˆ’π‘ + 𝐡𝑉1( 4 βˆ’ 2)+ 𝐴𝑆 𝑁 ( 4 βˆ’ 1) + ( 5 βˆ’ 8)𝛿1 + (1βˆ’π‘’1(𝑑))(1βˆ’π‘’2(𝑑))𝛽2𝑉1 𝑁 ( 2 βˆ’ 4) + ( 5 βˆ’ 7)(πœ‘1 + 𝑒4(𝑑)) + (1βˆ’π‘’1(𝑑))𝛽1𝑆 𝑁 ( 1 βˆ’ 4)+ ( 5 βˆ’ 6)𝛼 + 5πœ‡, π‘‘πœ6 𝑑𝑑 = βˆ’ πœ•π» πœ•πΌ = βˆ’π‘ + 𝐡𝑉1( 4 βˆ’ 2)+ 𝐴𝑆 𝑁 ( 4 βˆ’ 1)+ 6(πœ‡ + 𝑑1) + (1βˆ’π‘’1(𝑑))(1βˆ’π‘’2(𝑑))𝑛1𝛽2𝑉1 𝑁 ( 2 βˆ’ 4)+ ( 6 βˆ’ 7)πœ‘2 + (1βˆ’π‘’1(𝑑))𝑛1𝛽1𝑆 𝑁 ( 1 βˆ’ 4)+ ( 6 βˆ’ 8)𝛿2, π‘‘πœ7 𝑑𝑑 = βˆ’ πœ•π» πœ•π½ = βˆ’π‘‘ + 𝐡𝑉1( 4 βˆ’ 2) + 𝐴𝑆 𝑁 ( 4 βˆ’ 1)+ 7(πœ‡ + 𝑑2 ) + (1βˆ’π‘’1(𝑑))(1βˆ’π‘’2(𝑑)) 𝑛2𝛽2𝑉1 𝑁 ( 2 βˆ’ 4)+ 8πœ‡ + ( 7 βˆ’ 8)𝛿3 + (1βˆ’π‘’1(𝑑))𝑛2𝛽1𝑆 𝑁 ( 1 βˆ’ 4), π‘‘πœ8 𝑑𝑑 = βˆ’ πœ•π» πœ•π‘… = 𝐡𝑉1( 4 βˆ’ 2) + 𝐴𝑆 𝑁 ( 4 βˆ’ 1), } (11) where 𝐴 = (1βˆ’π‘’1(𝑑))𝛽1(𝑃+𝑛1𝐼+𝑛2𝐽) 𝑁 and 𝐡 = (1βˆ’π‘’1(𝑑))(1βˆ’π‘’2(𝑑))𝛽2(𝑃+𝑛1𝐼+𝑛2𝐽) 𝑁2 with tranversality conditions 1(𝑑𝑓) = 2(𝑑𝑓) = 3(𝑑𝑓) = 4(𝑑𝑓) = 5 (𝑑𝑓) = 6(𝑑𝑓) = 7(𝑑𝑓) = 8(𝑑𝑓) = 0. (12) Furthermore, the respective controls, 𝑒1 βˆ—,𝑒2 βˆ—,𝑒3 βˆ—,𝑒4 βˆ— are obtained by solving πœ•π» πœ•π‘’1 = 0, πœ•π» πœ•π‘’2 = 0, πœ•π» πœ•π‘’3 = 0, πœ•π» πœ•π‘’4 = 0 and these are given by C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega 𝑒1 βˆ— = (𝑃+𝑛1𝐼+𝑛2𝐽)(𝛽1𝑆(𝜁4βˆ’ 𝜁1)+(1βˆ’π‘’2(𝑑))𝛽2𝑉1(𝜁4βˆ’ 𝜁2)) π‘š1𝑁 , 𝑒2 βˆ— = (𝑃+𝑛1𝐼+𝑛2𝐽)(1βˆ’π‘’1(𝑑))𝛽2𝑉1(𝜁4βˆ’ 𝜁2) π‘š1𝑁 + (𝜁1βˆ’πœ2)πœ€1𝑆 π‘š2 , 𝑒3 βˆ— = (𝜁2βˆ’πœ3)πœ€2𝑉1 π‘š3 , 𝑒4 βˆ— = (𝜁5βˆ’πœ7)𝑃 π‘š4 . With the controls 𝑒1 βˆ—,𝑒2 βˆ—,𝑒3 βˆ—,𝑒4 βˆ—, the optimality condition is given by 𝑒1 π‘œπ‘π‘‘ = π‘šπ‘Žπ‘₯{0 ,π‘šπ‘–π‘›(1 ,𝑒1 βˆ—)}, 𝑒2 π‘œπ‘π‘‘ = π‘šπ‘Žπ‘₯{0 ,π‘šπ‘–π‘›(0.95 ,𝑒2 βˆ—)}, 𝑒3 π‘œπ‘π‘‘ = π‘šπ‘Žπ‘₯{0 ,π‘šπ‘–π‘›(0.95 ,𝑒3 βˆ—)}, 𝑒4 π‘œπ‘π‘‘ = π‘šπ‘Žπ‘₯{0 ,π‘šπ‘–π‘›(1 ,𝑒4 βˆ—)}. } (13) The optimality system consists of the state system (8), the adjoint system (11) with initial conditions of (3) and transversality condition (12) together with the characterization of the optimality condition (13). The restrictions of obtaining the uniqueness of the optimal control based on the length of time follow the approach in [2, 9, 14]. 5. Numerical simulations In this section, the solutions of the optimality system are solved numerically using the forward and backward fourth-order Runge-Kutta method that is coded in MatLab software. The parameter values in Table 1 with the constants 𝑏 = 𝑐 = 𝑑 = 100,π‘š1 = 10000,π‘š2 = 2000, π‘š3 = 2000,π‘š4 = 5000 and the initial conditions, 𝑆(0) = 200000, 𝑉1(0) = 2000, 𝑉2(0) = 1800, 𝐸(0) = 80, 𝑃(0) = 60, 𝐼(0) = 100, 𝐽(0) = 20, 𝑅(0) = 10000 are used for the numerical simulations purpose. 5.1 Discussion Figure 4 shows the population dynamics of infected persons in the prodromal stage, 𝑃(𝑑), infected persons in the rash stage, 𝐼(𝑑), isolated persons, 𝐽(𝑑), for with and without control and the control profile. According to Figure 4π‘Ž, with control measures, measles- free population is achieved for 𝑃(𝑑) population faster, and thus reducing the number of persons moving to the infected people in the rash stage, while Figure 4b, the number of infected persons in the rash stage, 𝐼(𝑑), decrease to zero within 25 weeks with control measures in place. Also, Figure 4𝑐 reveals that with the implementation of the control measures, there is a sharp increase in the number of isolated persons before decreasing to zero by 25 weeks and achieves measles-free population. Controlling measles transmission dynamics with optimal control analysis Figure 4. The population dynamics of (a) infected persons in the prodromal stage, 𝑃(𝑑), (b) infected persons in the rash stage, 𝐼(𝑑), (c) Isolated persons, 𝐽(𝑑), (d) Controls, 𝑒2, 𝑒3, and (e) Controls, 𝑒1, 𝑒4. Here, W/C means β€œWith Control” while W/O/C means β€œWithout Control”. 0 50 100 0 500 1000 1500 2000 Time (Weeks) P (t ) (a) W/C W/O/C 0 50 100 0 50 100 Time (Weeks) I( t) (b) W/C W/O/C 0 50 100 0 20 40 60 Time (Weeks) J (t ) (c) W/C W/O/C 0 50 100 0 2 4 6 8 x 10 -4 Time (Weeks) C o n tr o l p ro fi le (d) u 2 u 3 0 10 20 30 40 50 60 70 80 90 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Time (Weeks) C o n tr o l p ro fi le (e) u 1 u 4 C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega Figure 5. The population dynamics of (a) infected persons in the prodromal stage, 𝑃(𝑑), (b) infected persons in the rash stage, 𝐼(𝑑), (c) Isolated persons, 𝐽(𝑑) when triple controls are implemented together. Here, the numbers 1,2,3, π‘Žπ‘›π‘‘ 4, are subscripts of the control functions, 𝑒1,𝑒2,𝑒3,𝑒4 while W/O/C means β€œWithout Control”. Figure 6. Control profile for implementation of triple optimal controls. 0 50 100 0 500 1000 1500 2000 (a) 123 124 134 234 W/O/C 0 50 100 0 50 100 Time (Weeks) I( t) (b) 123 124 134 234 W/O/C 0 50 100 0 20 40 60 Time (Weeks) J (t ) (c) 123 124 134 234 W/O/C 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 1.5 x 10 -4 Time (Weeks) C o n tr o l p ro fi le u 4 =0 u 2 u 3 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 Time (Weeks) u 1 u 4 =0 u 1 Controlling measles transmission dynamics with optimal control analysis The control profile for achieving the result in Figures 4a-4c are displayed in Figures 4d and 4e. They show that the upper bounds for 𝑒1,𝑒2,𝑒3 are 9.9, 6.1 Γ— 10 βˆ’4 and 2 Γ— 10βˆ’5, respectively, where the control, 𝑒3 maintains a bound of 6.9 for 50 weeks before it gradually increases to 0.9 as at 90 weeks. For without control measures, Figures 4a – 4c show the endemicity of the measles infection in the population. In Figure 5, the implementation of triple control measures for the dynamics of the infected compartments (𝑃(𝑑),𝐼(𝑑),𝐽(𝑑)) are evaluated. We observed in Figures 5a -5b that simultaneous implementation of any triple control measures reduce the number of infected persons (𝑃(𝑑),𝐼(𝑑)) in the population as they achieve a measles-free population within a short time while for isolated persons, 𝐽(𝑑), the combine implementation of 𝑒1,𝑒2,𝑒3(123) yields a faster and better result in achieving a measles-free population compared with other combinations (see Figure 5c). With this, it implies that combined implementation of control measures, 𝑒1,𝑒2,𝑒3(123), reduces the number of infected persons in the prodromal stage, 𝑃(𝑑), rash stage, 𝐼(𝑑) and the isolated persons, (𝐽(𝑑)) compare with any other combination of control measures. The control profile for triple control measures are display in Figure 6. The control profile when 𝑒4 = 0 is the combined implementation of 𝑒1,𝑒2,𝑒3(123) that gives the best result in Figure 5, which indicates that mass distribution of nutritional (supplement) support, administration of first and second dose vaccine control measures have much effect on controlling measles in the population. To achieved this, 𝑒1 maintains an upper bound that declines after 85 weeks, whereas 𝑒2 maintains a bound of 1.2 Γ— 10 βˆ’4 that decreases gradually till 85 weeks where it declines to the final time. For 𝑒3, it starts with a bound of 3.2 Γ— 10 βˆ’5 that slightly increases to 4.0 Γ— 10βˆ’5 at 70 weeks before declining to the final time. The numerical simulations imply that combined implementation of mass distribution of nutritional support, complete vaccination with the first and second dose of vaccine and isolation of infected persons in the prodromal stage will help eradicate the spread of measles in the population. This is in agreement with the sensitivity analysis result and the results in [3]. This indicates that implementation of control measures will help prevent the spread of measles infection in the population. However, if there are limited facilities to isolate the infected persons in the prodromal stage, the triple control measures, mass distribution of nutritional support and complete vaccination with first and second doses of vaccine will reduce the spread of measles infection as fewer people will be infected and thus help the health practitioners achieve the best strategy in the control of the spread of measles in the community. 6. Conclusion In this paper, an autonomous system for the transmission dynamics of measles disease involving isolated persons and two doses of vaccination is formulated. The model disease- free equilibrium and basic reproduction number (𝑅0) are computed. The sensitivity analysis of the basic reproduction number, which includes the pairwise comparison and scatterplots of important parameters of the basic reproduction number is carried out using Latin Hypercube Sampling (LHS) scheme. LHS scheme is also used to compute and C. E. Madubueze, I. O. Onwubuya, and I. Mzungwega compare the values of Partial Rank Correlation Coefficients (PRCCs) of the model parameters. The result of the sensitivity analysis indicates that transmission rates, first and second-dose vaccination rates and isolation rate of the infected persons in the prodromal stage are significant parameters in eradicating the spread of measles infection. Furthermore, the optimal control model of the autonomous system is developed and analysed with four control measures, mass distribution of nutritional support, administration of first and second dose vaccination and isolation of infected persons in the prodromal stage. From the numerical simulations, we found out that the combined implementation of the four control measures achieves a measles-free population on time than without control measures. However, if there are limited facilities to isolate the infected persons in the prodromal stage, the triple control measures, mass distribution of nutritional support and complete vaccination will reduce the spread of measles infection. Thus, this offers the public health practitioners the best strategy that can control the spread of measles in the community. References [1] S. O. Adewale, A. I. Olopade, S. O. Ajao, G. A. Adeniran. Optimal control analysis of the dynamical spread of measles. 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