The Impact of Public Health Interventions on The First and Second Waves of COVID - 19 in Trinidad And Tobago–A Simple Epidemic Model

Introduction
The COVID-19 pandemic has resulted in more than 35 million confirmed cases worldwide. Currently, there is no specific treatment for the disease or available vaccine to reduce the spread of COVID-19. As such, countries rely on a range of public health interventions to assist in halting the spread of transmission. Caribbean countries have also adopted many public health interventions. In this paper, we use mathematical modelling to demonstrate the impact of public health interventions on the progression of COVID-19 in order to provide timely decision support.

Methods
A cohort Markov model, based on the concept of the SEIR model, was built to reflect the characteristics of the COVID-19 virus. Five possible public health interventions in the first wave and a projection of current second wave were simulated using the constructed model. 

Results
The model results indicate that the strictest combined interventions of complete border closure and lockdown were the most effective with the number of deaths less than ten in the first wave. For the current second wave, it will take around 30 days for the pandemic to pass its peak after implementing the wearing of face masks policy.

Conclusions
This paper shows the impact of common public health interventions on the COVID-19 pandemic, using Trinidad and Tobago as an example. Such impacts may be useful in reducing delays in decision-making and improving compliance by populations. However, given the limitations associated with mathematical models, decision-making should be guided by economic assessments, infectious disease and public health expertise.


Introduction
The COVID-19 pandemic has resulted in more than 35 million confirmed cases worldwide. Currently, there is no specific treatment for the disease or available vaccine to reduce the spread of COVID-19. As such, countries rely on a range of public health interventions to assist in halting the spread of transmission. Caribbean countries have also adopted many public health interventions. In this paper, we use mathematical modelling to demonstrate the impact of public health interventions on the progression of COVID-19 in order to provide timely decision support.

Methods
A cohort Markov model, based on the concept of the SEIR model, was built to reflect the characteristics of the COVID-19 virus. Five possible public health interventions in the first wave and a projection of current second wave were simulated using the constructed model.

Results
The model results indicate that the strictest combined interventions of complete border closure and lockdown were the most effective with the number of deaths less than ten in the first wave. For the current second wave, it will take around 30 days for the pandemic to pass its peak after implementing the wearing of face masks policy. This is an open access article under the terms of the Creative Commons Attribution License which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

INTRODUCTION
The novel coronavirus, called SARS-CoV-2, has now resulted in a pandemic causing the disease COVID-19. 1 The number of confirmed cases globally has surpassed 35 million with more than 1,000,000 deaths. 1 The first case of COVID-19 was confirmed in the Caribbean region on March 1 st 2020. 2 To date (October 12 th 2020), 33 Caribbean countries have registered cases with over 200,000 confirmed cases and almost 4000 deaths in the region. 3 The high transmissibility of the COVID-19 virus, its subsequent potential to quickly overwhelm a country's health system, the lack of treatment and an available vaccine creates an extremely uncertain situation. As such, many countries rely on the implementation of public health interventions as an approach to slow the spread of the disease. These public health interventions include border closures, school closures, social distancing measures such as reducing crowding, mass gatherings, physical distancing and health-related behavioural modifications such as hand washing, cough/sneeze etiquette and wearing of face masks. 4,5 Caribbean countries have adopted similar approaches, implementing a range of interventions including border control and the most extreme form of social distancing, lockdowns. 6 Knowledge of the potential impact of the interventions may reduce delays in implementation by decision makers and promote compliance by the public.
In order to demonstrate such impacts, we used the example of Trinidad and Tobago, a Caribbean country with a population of approximately 1.3 million people, 7 to construct a simple epidemic and strategy model based on the demographics of Trinidad and Tobago and the characteristics of the COVID-19 virus. This paper aims to discuss how public health interventions impacted the progression of COVID-19 in both first and second waves, using the simple epidemic model to highlight key areas.
The purpose of the model is to demonstrate the magnitude of disease spread and the importance of public health interventions rather than to predict the actual number of confirmed cases and deaths.

Epidemic and strategy model
The model was built based on the concept of the SEIR    Table 1. [10][11][12][13][14][15][16][17][18][19][20][21][22] All the percentage information were transformed to rates (cases per day) before inserting them into the model. S notes susceptible individuals, exposed individual noted by E, infected individual noted by I and recovered individuals noted by R. The equations calculated the number of people in each health state today (n) based on the number yesterday (n-1) and the rates of change such as α, β and , where α is the rate of recovery, β is the rate of infection and is the reverse of incubation period. The above-mentioned equations were implemented in Excel and the cohort were moved from a state to another followed the standard process described by Briggs. 23 For simplicity, several assumptions were made about the model. These include the following: 2. The reproduction number, detection rate and transition rates were constant.
3. There were unlimited healthcare resources. Aside from the confirmed cases, undiagnosed infected cases also exist. These included those persons who were asymptomatic and those who were symptomatic but did not require or seek medical attention. These persons may not be officially recorded and as a result may transmit

Value
Source Note

Rate of imported cases
Number of actual detected cases at the airport from 1 March to 1 April 90 (10) Detect rate at the airport 0.6 assumption

Model parameters
S = initial number of susceptible population 1363985  In the second wave model, the model was able to reproduce the number of confirmed cases and deaths which were found to be similar to the actual reported figures for the first 30 days (Figure 3). The estimated increased number of confirmed cases from 3 rd September to 3 rd October was around 2,600 (2,731 confirmed based on national reports) and the increased number of deaths was around 75 (less than 70 based on confirmed national reports). 24 If this trend continues with no unexpected imported cases and the same restrictions remain implemented, it is theoretically possible that the local spread will be at a negligible level in early 2021 ( Figure   3).

Public health interventions and potential challenges
In this paper, we used Trinidad and Tobago as an   Real-time public communication, another form of information technology, may also be used for public health education purposes. 25,27 This strategy has shown that delivering simple and vital health education information using SMS text messages can provide the public with effective guidance for prevention of COVID-19, assisting with the location of nearby testing centres and combatting misinformation.  Without an available vaccine, widespread testing and surveillance of populations is also considered an option for controlling the spread of disease from those who are undiagnosed or asymptomatic. 29 Such interventions may allow governments to identify these 'silent' infected individuals and subsequently apply corresponding interventions to stop/break the chain of transmission. The importance of managing and controlling 'silent' cases is demonstrated in Figure 2 with the public health interventions resulting in low numbers of deaths and infections. However, widespread testing and surveillance of populations is also not without its limitations. 29,30 The financial burden of widespread testing may be an issue as such an initiative requires manpower, sufficient personal protective equipment and testing kits, all of which are currently limited. 30 A more effective and efficient intervention may be rapid identification of clusters of cases or super-spreaders through contact tracing. 31 The wearing of face masks is another measure whose  forthcoming with information). [35] Since these behavioural factors were not taken into account in our model, this may affect the projected impact of interventions.
In order to provide decision makers with more reliable information to support informed decisions, a more comprehensive epidemiology and strategy model (compared to our hypothetical model) is required. This model should (1) take into account the local geography and human mobility patterns, (2) consider the structure of the medical system and healthcare resources available, (3) combine public health strategy and economic assessment, (4) predicate the impact of interventions on the trajectory of a disease. Such models should also be accompanied by studies that explore behavioural factors.
Altogether, this should assist complex pandemic planning.

CONCLUSION
In conclusion, this paper shows the impact of common public health interventions on the COVID-19 pandemic in Trinidad and Tobago, using a simple epidemic model.
Pandemic planning and response is a complex process.
Decisions regarding effectiveness of interventions to limit the spread of disease should be guided by the use of reliable epidemiology models, economic assessments, behavioural studies, infectious disease and public health expertise in order to manage this pandemic as well as future pandemics.