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This study aimed to optimize the inkjet printing process for the fabrication of rGO- based lactate biosensors. The ink used for printing possessed proper fluidic properties, and the droplets were connected on the film by repeated printing process. The ink also contained ethyl cellulose, which reduced the coffee ring effect and resulted in a uniform film of rGO. The optimal density of Anti-L on the surface of the sensor was found to be 200 mM, and the incubation time for lactate samples was optimized to 60 minutes. The device showed linear responses from 100 to 500 μM with a high sensitivity of about 0.5 per 100 μM lactate and a low detection limit at 23 μM at S/N=3. This study demonstrates that optimized inkjet printing can be used to fabricate highly sensitive lactate biosensors for various applications.

Introduction. Cataract is the leading cause of blindness. About 90% of cataract blindness occurs in low- and middle-income countries. The prevalence of blindness and low vision in any country depends on the socioeconomic status, the availability of medical and healthcare facilities, and the literacy of the population. Aim: This paper aims to estimate the cataract surgery rate (CSR) at Pusat Pembedahan Katarak, MAIWP-Hospital Selayang (Cataract Operation Centre), and provide descriptive assessments of the patients who received eye treatments in the center. Methods: The data were retrieved from the clinical database from 2013 to 2016. Information on the patient’s sociodemographic and clinical and treatment history was collected. Results: The cataract surgery rate for 2013 was about 27 and increased to 37.3 in 2014. However, it declined to 25 in 2015 before it resumed to 36 in 2016. For female patients who received eye treatments at Pusat Pembedahan Katarak, MAIWP-Hospital Selayang, the rate was higher (53.7%) compared to male patients (46.3%). The mean duration of cataract surgery from 2013 to 2016 was 21.25 ± 11.071 min. Conclusion: The increased cataract surgery rate for MAIWP-HS through smart partnerships for day care cataract surgery proved that better accessibility makes the short- and long-term strategies for the reduction and prevention of blindness in Malaysia possible to achieve.

There is currently no specific evidence regarding the exact etiology of anal fissures. However, various management options were reported and validated among the relevant research. Lateral internal sphincterotomy has been validated among relevant investigations in the literature as a valid modality for managing patients with chronic anal fissures. In the present literature review, we formulated evidence based on these studies to compare open and closed techniques of this surgery according to the reported outcomes. However, evidence regarding the superiority of either of the techniques over the other is not consistent among these investigations. For instance, some studies reported that closed sphincterotomy is more favorable than the open approach and should be considered the treatment choice for chronic anal fissures. This is because the technique is associated with less frequent rates of complications, less expensive, safe, and effective. On the other hand, many other relevant studies also demonstrated that the reported outcomes for the two modalities exhibited non-significant differences. Therefore, we suggest that researchers should furtherly conduct additional investigations before drawing any conclusions in this field.

Background: According to increasing concern about the COVID-19 pandemic and the risk of smoking this study was conducted to find the effect of health measures during the COVID-19 pandemic on smoking dependence & passive smoking. Methods: A cross-sectional study was conducted in September 2020, by using a valid and reliable questionnaire, the data were analyzed by using SPSS, version 20 software. Results: The study showed 16.9% of participants increased their nicotine use and 12.4% decreased their nicotine use. Despite no significant change in smoking dependence, we found that smokers who used to smoke more than 30 cigarettes per day before the quarantine increased by two folds. In addition, we found that smokers who awaken at night sometimes to have cigarettes before quarantine had increased markedly by 50% during quarantine. Furthermore, smokers who had an extreme urge to smoke over the week before the quarantine have elevated markedly during the quarantine from 31 smokers to 60. Also, over 35.2 % of surveyed individuals experienced a rise in smoking desire during the quarantine. Regarding passive smoking, the surveyed individuals reported a generally slight decline in exposure to secondhand smoking. However, the number of exposed individuals to smoking for more than 8 hours increased by 27%. Conclusion: During the lockdown, individuals smoked marginally more cigarettes compared to the periods before the lockdown with no significant change in smoking dependence. There was a slight decline in exposure to secondhand smoking. However, the number of exposed individuals to household smoking for more than 8 hours had been increased.

Ghada H Naguib,1,2 Gamal S Abd El-Aziz,3 Hisham A Mously,4 Wafaa A Alhazmi,5 Abeer M Alnowaiser,6 Ali H Hassan,7 Mohamed T Hamed4,8 1Department of Restorative Dentistry, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia; 2Department of Oral Biology, Faculty of Dentistry, Cairo University, Cairo, Egypt; 3Department of Anatomy, Faculty of Medicine, King Abdulaziz University, Jeddah, Saudi Arabia; 4Department of Oral and Maxillofacial Prosthodontics, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia; 5Department of Medical Laboratory Sciences, Faculty of Applied Medical Sciences, King Abdulaziz University, Jeddah, Saudi Arabia; 6Department of Pediatric Dentistry, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia; 7Department of Orthodontics, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia; 8Department of Fixed Prosthodontics, Faculty of Dentistry, Cairo University, Cairo, EgyptCorrespondence: Mohamed T HamedDepartment of Oral and Maxillofacial Prosthodontics, Faculty of Dentistry, King Abdulaziz University, P.O.Box 80209, Jeddah, 21589, Saudi ArabiaEmail mthamed@kau.edu.saPurpose: This in vitro study was undertaken to investigate the antimicrobial effect of distinctive oral mouth washes after the addition of zein-coated (Magnesium oxide) MgO nanoparticles on exemplary of some oral microorganisms.Materials and Methods: Three hundred and twelve samples were used in this study. A set of five concentrations of MgO nanoparticles with zein and without zein-coating were incorporated into three oral mouth washes: Listerine zero, Listerine total control and Oral B in the mass percentages of 0.3%, 0.5%, 1%, 2%, 5% and 10%, in addition to controls with no MgO nanoparticles. The antimicrobial effect of three mouth washes with variable concentrations of MgO was tested against the following organisms: Staphylococcus aureus, Streptococcus mutans, Enterococcus faecalis and Candida albicans using the disc diffusion test (DDT) and direct contact test (DCT). Data were analyzed using one-way ANOVA statistical test.Results: The tested mouthwashes with zein-coated MgO nanoparticles showed significant differences of antimicrobial activity on S. mutans, S. aureus, E. faecalis, and C. albicans in the disc diffusion test. While in the DCT, all tested mouthwashes with MgO nanoparticles with and without zein coating showed antimicrobial activity on all tested microorganisms.Conclusion: Zein-coated MgO nanoparticles may be considered as a potential antimicrobial agent when added to oral mouthwashes. Future analysis, including in vivo studies, is required in order to incorporate zein/MgO nanoparticles into oral mouthwashes that may improve its antibacterial property.Keywords: MgO, nanoparticles, zein polymer, antibacterial, mouthwash

Historically, the majority of oncology clinical trials are conducted in Western Europe and North America. Globalization of drug development has resulted in sponsors shifting their focus to the Asia-Pacific region. In Malaysia, implementation of various government policies to promote clinical trials has been initiated over a decade ago and includes the establishment of Clinical Research Malaysia, which functions as a facilitator and enabler of industry-sponsored clinical trials on a nationwide basis. Although oncology clinical trials in Malaysia have seen promising growth, there are still only a limited number of early phase oncology studies being conducted. Hence, the Phase 1 Realization Project was initiated to develop Malaysia's early phase clinical trial capabilities. In addition, the adaptation of good practices from other countries contribute to the effective implementation of existing initiatives to drive progress in the development of early phase drug development set up in Malaysia. Furthermore, holistic approaches with emphasis in training and education, infrastructure capacities, strategic alliances, reinforcement of upstream activities in the value chain of drug development, enhanced patient advocacy, coupled with continued commitment from policy makers are imperative in nurturing a resilient clinical research ecosystem in Malaysia.

Historically, the majority of oncology clinical trials are conducted in Western Europe and North America. Globalization of drug development has resulted in sponsors shifting their focus to the Asia-Pacific region. In Malaysia, implementation of various government policies to promote clinical trials has been initiated over a decade ago and includes the establishment of Clinical Research Malaysia, which functions as a facilitator and enabler of industry-sponsored clinical trials on a nationwide basis. Although oncology clinical trials in Malaysia have seen promising growth, there are still only a limited number of early phase oncology studies being conducted. Hence, the Phase 1 Realization Project was initiated to develop Malaysia's early phase clinical trial capabilities. In addition, the adaptation of good practices from other countries contribute to the effective implementation of existing initiatives to drive progress in the development of early phase drug development set up in Malaysia. Furthermore, holistic approaches with emphasis in training and education, infrastructure capacities, strategic alliances, reinforcement of upstream activities in the value chain of drug development, enhanced patient advocacy, coupled with continued commitment from policy makers are imperative in nurturing a resilient clinical research ecosystem in Malaysia.

Objective: The present study explains the success and failure of dental implant diameter on the efficiency of fatigue by conducting a systematic review analysis. Methods: An extensive literature search was conducted to carry out systematic review using different scholarly platforms and libraries. A total of 12 studies published within the past 20-year time (1999-2019) were included following the inclusion and exclusion criteria based on the PRISMA guidelines. Additionally, the study outcomes were evaluated to determine their perceptions regarding the role of dental implant diameter in influencing the implant’s fatigue performance. Results: The implant diameter can be categorized into wide diameter (5-6 mm), regular diameter (3.75-4 mm), and small/narrow diameter (3-3.4 mm). The narrow diameter implants are indicated through thin alveolar ridges and mesiodistal spaces (less than 7 mm). The implants with narrow diameter would offer greater risk of fatigue failure for clinical situations with significant functional loading. No significant differences were found either in success or failure of dental implant diameter on fatigue efficiency after 1-year and 3-year follow-up. Conclusion: The technical complication of dental implant include abutment screw loosening or fracture, abutment and superstructure fracture, and implant body fracture. The study has study has mainly focused on the impact of dental implant diameter on the efficiency of fatigue and reviewed a significant impact of dental implant diameter on the fatigue efficiency. Keywords: Dental Implants, Efficiency, Perception. Continuous...

Introduction: Recently, zein-coated MgO nanowires were synthesized, which could be promising as an effective antimicrobial compounds that can be combined in the preparation of a diversity of new dental formulations. However, there is a deficiency of information concerning their toxicological profile regarding the human health. Objective: This in vivo study aimed to explore the hepato- and nephrotoxicity of low versus high doses of zein-coated MgO nanowires in rats. Materials and Methods: A 21-day recurrent dose toxicity research was carried out. Wistar rats were divided into 2 main groups, males and females (n = 18). Each group was further subdivided into 3 subgroups: control, MgO-zein nanowires low dose, MgO-zein nanowires high dose. The low dose used was 100 mg/kg while the high dose used was 200 mg/kg. Results: The results showed that MgO-zein nanowires at both doses did not affect the electrolytes levels compared to the control levels. Also, they did not produce any significant alteration in liver function markers in both rats' genders. MgO-zein nanowires at both doses did not produce any effective alteration in serum creatinine in treated rats of both genders. Moreover, very minimal histological alterations were observed in both doses of MgO-zein nanowires in liver and kidney of both genders. Conclusion: Based on the observed safety of zein-coated MgO nanowires, it can be utilized as an effective antimicrobial compound that can be combined in the preparation of a diversity of new dental formulations.KEY MESSAGESMgO NPs are globally used in multiple fields including the therapeutic field.Zein has wide pharmaceutical applications especially coating the tablet over sugar.There are no cytotoxic studies that investigate MgO-zein nanowires safety until now.

Purpose Dental implant is an effective and standardized treatment procedure in the healthcare setting. This study presents a comparison of dental implant reconstruction using screw and cement. It explicitly reviews the studies concerning cement and screws dental implants to determine the efficiency of the two. Patients and methods A systematic review was conducted by comprehensively searching electronic literature. The keywords, such as "Screw versus Cement Retained Fixed Implant Supported Reconstructions," "Screw Retained Fixed Implant." "Cement Implant" and "Dental Implant" were used for article searching. Twelve studies were included based on the determined inclusion and exclusion criteria. Results No significant difference was found between the screw-retained and cemented retained implant supported reconstructions. Dental implants are associated with complications leading to implant failure based on the type of restoration that is being used; cement-retained restoration and screw-retained restoration. The treatment selection must be based on the significance criteria and the tooth condition. Conclusion Screw-retained implant-supported reconstructions were found to pose less biological and technological complications. Retention of the tooth is more stable and functional when implantation is selected based on the efficiency of a treatment procedure.

ObjectivesTo develop consensus statements regarding the regional-level or district-level distribution of surgical services in low and middle-income countries (LMICs) and prioritisation of service scale-up.DesignThis work was conducted using a modified Delphi consensus process. Initial statements were developed by the International Standards and Guidelines for Quality Safe Surgery and Anesthesia Working Group of the Global Alliance for Surgical, Obstetric, Trauma and Anesthesia Care (G4 Alliance) and the International Society of Surgery based on previously published literature and clinical expertise. The Guidance on Conducting and REporting DElphi Studies framework was applied.SettingThe Working Group convened in Suva, Fiji for a meeting hosted by the Ministry of Health and Medical Services to develop the initial statements. Local experts were invited to participate. The modified Delphi process was conducted through an electronically administered anonymised survey.ParticipantsExpert LMIC surgeons were nominated for participation in the modified Delphi process based on criteria developed by the Working Group.Primary outcome measuresThe consensus panel voted on statements regarding the organisation of surgical services, principles for scale-up and prioritisation of scale-up. Statements reached consensus if there was ≥80% agreement among participants.ResultsFifty-three nominated experts from 27 LMICs voted on 27 statements in two rounds. Ultimately, 26 statements reached consensus and comprise the current recommendations. The statements covered three major themes: which surgical services should be decentralised or regionalised; how the implementation of these services should be prioritised; and principles to guide LMIC governments and international visiting teams in scaling up safe, accessible and affordable surgical care.ConclusionsThese recommendations represent the first step towards the development of international guidelines for the scaling up of surgical services in LMICs. They constitute the best available basis for policymaking, planning and allocation of resources for strengthening surgical systems.

Introduction: The proper screw preload delivery is affected by several factors, among which the coefficient of friction is responsible for affecting the delivery of proper amount of preload torque. It is believed that the delivered preload increases due to reduction in coefficient of friction. Aims: The study aims to investigate maximum von Misses equivalent stresses generated within different parts of the assembly of ɸ 4.1 mm and 10 mm long Straumann implant. Material and Methods: The implant is inserted in place of the mandible first molar because of tightening screw. An analysis considered the screw surfaces as frictional and concluded that the frictional moment and the axial force opposed the advancement of the screw during its tightening. These loads were utilized for the implementation of three-dimensional finite element linear stress-strain analysis to compute the maximum equivalent stress generated within each part of the implant assembly to compare with the yield stress material of that part. The material used for retaining screw and the coefficient of friction between the screw surfaces were the variables of the study, including the abutment and implant surfaces. Results and Discussion: Results were obtained for two assemblies having type III gold and Ti-6Al-4V titanium alloy screws each with 14 values of the friction coefficient. Conclusion: The study concluded that stresses at the maximum tightening moment applied on the screw invariably decrease due to an increase in the coefficient of friction for all assembly parts.

Introduction: The tightening of the retaining screw helps in the insertion of implant at the mandible of first molar. Moreover, the calculation of the external loads acting on the screw head during its tightening and release need to be devised. Aims: The study aims to predict the fatigue life of a retaining abutment screw used in dental implant. Material and Methods: A typical straumann implant, inserted in place of missing first mandible molar was selected. 3D finite element stress analysis tool was used to evaluate the normal occlusion between the restoration crown and the opposing maxillary tooth. The mastication force acting mutually on the two teeth was simulated during the time of the occluding phase of the chewing process. Results and Discussion: The fatigue damage parameter experienced at contact time was 206.5 ms by the most stressed site within the retaining screw that was plotted against the magnitude of the chewing force. The fatigue damage the parameter is below the Ti-6AI 4V threshold value for chewing force greater than 809 N. Findings of the study were provided considering the two assemblies consisting of Ti-6Al-4V titanium alloy, followed by type III gold of screws with the friction coefficient of each from the overall 14 values. Conclusion: Considering the findings of the study, it is concluded that the release of the tightening moment of the wrench resulted in generating the equivalent stress. Results further concluded that the increase in coefficient friction on all the assembly parts resulted in the expansion of the stress followed by the increase in the wrenching tightening moment.

The untightening resistance has a negative impact on the stability of implant-abutment system. However, there is a need to retighten the screws periodically. Aim: This study aims to compare the stress level on the dental implants before and after tightening of the screw. Methods: A 3D geometrical idealization was constructed in place of a missing mandible first molar of an adult. An integrated retaining screw was fixed to a standard Ti-6Al-4V abutment after osseointegration. Model’s geometry was exported to generate threedimensional mesh. Results: The results were acquired with 14 values of the friction coefficient for type III gold and Ti-6Al-4V titanium alloy screws. There was variation in values of gold screw before tightening; however, it was considerably low as compared to the corresponding values in the case of titanium screw. Moreover, the magnitudes of Pa of gold screw were less as compared to the titanium screw. There is a decrease in stresses at maximum tightening moment because of increase in coefficient of friction for assembling different parts. Moreover, the magnitudes of Pa of gold screw were less as compared to the titanium screw. Conclusion: The invariable decrease in the release of wrench tightening moment was due to the increase on the wrench tightening moment. Moreover, the decrease in the stresses at maximum tightening moment applied to screw was because of increase in coefficient of friction for assembling different parts.

Tobacco cigarette smoking is a well-established risk factor for oral diseases, especially periodontal diseases. Over the past few years, electronic cigarettes (or "E-cigarettes") have gained popularity. There is some evidence that e-cigarettes may play a role in helping people quit smoking, and they are occasionally seen as a less dangerous alternative to tobacco use. However, there are worries about their effects on health, notably in terms of oral health and the emergence of periodontal disease. Limited information is available regarding the effect on oral disease. E-cigarettes come in a variety of nicotine strengths and flavoring combinations, all of which have been associated with detrimental oral health issues. A growing body of research supports the idea that vaping or using electronic cigarettes may increase the chance of developing oral health problems such as tooth decay, gum disease, periodontal disease, cracked or broken teeth, and pain in the tongue or inside of the cheek. Even if e-cigarettes were less harmful, they still could lead to the development of periodontal diseases through the decreased antioxidant capacity of saliva, the inflammatory effect, cell injury, and impaired reparability. High levels of nicotine content and menthol-favoring additives increase risk of periodontal damage in e-cigarette users. However, conflicting study results are also published for smokers who transitioned to e-cigarettes. Even though benefits or value of e-cigarettes as a substitute for tobacco cigarettes are still unknown, their impact on periodontal and general health status is still prominent.

Malaysia rolled out a diverse portfolio of predominantly three COVID-19 vaccines (AZD1222, BNT162b2, and CoronaVac) beginning 24 February 2021. We evaluated vaccine effectiveness with two methods, covering 1 April to 15 September 2021: (1) the screening method for COVID-19 (SARS-CoV-2) infection and symptomatic COVID-19; and (2) a retrospective cohort of confirmed COVID-19 cases for COVID-19 related ICU admission and death using logistic regression. The screening method estimated partial vaccination to be 48.8% effective (95% CI: 46.8, 50.7) against COVID-19 infection and 33.5% effective (95% CI: 31.6, 35.5) against symptomatic COVID-19. Full vaccination is estimated at 87.8% effective (95% CI: 85.8, 89.7) against COVID-19 infection and 85.4% effective (95% CI: 83.4, 87.3) against symptomatic COVID-19. Among the cohort of confirmed COVID19 cases, partial vaccination with any of the three vaccines is estimated at 31.3% effective (95% CI: 28.5, 34.1) in preventing ICU admission, and 45.1% effective (95% CI: 42.6, 47.5) in preventing death. Full vaccination with any of the three vaccines is estimated at 79.1% effective (95% CI: 77.7, 80.4) in preventing ICU admission and 86.7% effective (95% CI: 85.7, 87.6) in preventing deaths. Our findings suggest that full vaccination with any of the three predominant vaccines (AZD1222, BNT162b2, and CoronaVac) in Malaysia has been highly effective in preventing COVID-19 infection, symptomatic COVID-19, COVID-19-related ICU admission, and death.

Aim The utilization of fixed partial dentures (FPD) ceramic frameworks for replacing the missing posterior teeth is observed to have reported high failure rates. For this reason, 3-units FPD are designed and used extensively in the clinical practices, particularly for posterior mandibular region. The current study however, aims to carry out an evaluation of different stress patterns that are induced in a 3-units FPD within posterior part of mandible using finite element analysis (FEA). Materials and methods Different modalities of the implant-supported FPDs such as type of connector, length and diameter of implants were taken into account. A three-dimensional (3D) model simulation of a mandibular Kennedy class II removal partial denture (RPD) was designed from a computerized tomography (CT) input with digital imaging communication on medicine (DICOM) format. In addition, occlusal load of 100 N was also used for central fossae of first premolar, first molar and second molar of the 3-units' reconstruction for each model. The magnitude of von Mises stress including minimum stress, maximum stress and average stress were also evaluated for each loading condition. Results The findings of the current study showed evidence that tooth-implant design with a nonrigid connector has significantly increased the average stress. Furthermore, it was observed that rigid connector has considerably minimized the stress within the tooth-implant-supported FPD. Conclusion The study concluded that stress designs significantly influence the stress distribution around the bone. Clinical significance This study gives some guidance and criteria for the selection of the type of fixed implant prosthesis in the posterior mandibular region.

Issues associated with missing teeth can be found in almost all age groups. For edentulous patients, osseointegration is a highly efficient treatment. However, certain biochemical challenges are presented when osseointegrated implants are taken into consideration due to the periodontal ligament. Therefore, the current study focuses on clinical concerns that can occur with the use of dental implants and examines different trends of implant restoration and treatment of partial edentulous patients. Data were collected from ten research articles and analyzed by means of a qualitative secondary approach. The findings of the current study indicate that restoration and preservation of natural teeth are significant in the development of dental practices. Moreover, the determinant of endodontic treatment is considered to be a key factor in the retention and reconstruction of tooth functioning that is influenced by necrosis of dental pulp. We conclude that the osseointegration method is significant and highly effective for treating edentulous patients.

BACKGROUND: The aesthetics and strength of anterior porcelain layered zirconia (PLZ) crowns are mainly affected by the zirconia (Zr) coping design. There is a need for a modified design to enhance aesthetics with strength. OBJECTIVES: The purpose of this study was to compare the fracture resistance of anterior PLZ crowns having modified CAD-CAM Zr coping designs (in terms of thickness and marginal collar designs) with standard Zr copings. METHODS: Fifty PLZ crowns were fabricated and divided into two groups: Gr 1: Standard Zr Coping (SZC) (control gr) with 0.5 mm thickness (Facial-F, Mesial-M, Distal-D, incisal-I, and Palatal-P) without a collar; Gr 2: Collar Zr Coping (CZC) (test gr) with 2.5 mm collar height on M, D, P and 0.2 mm F and variable facial wall thickness. Subgroups: Gr 2a: (CZC-0.5 mm) facial wall thickness 0.5 mm; Gr 2b: (CZC-0.4 mm) facial wall thickness 0.4 mm; Gr 2c: (CZC-0.3 mm) facial wall thickness 0.3 mm; Gr 2d: (CZC-0.2 mm) facial wall thickness 0.2 mm. The fracture load was determined and analysed using One-way ANOVA and Dunnet test. RESULTS: The minimum fracture load was 927.36 ± 127.80 N observed for Gr 2c (CZC at 0.3 mm) while the maximum fracture load was 1373.61 ± 146.54 N observed for Gr 2a (CZC at 0.5 mm). A highly significant difference in mean fracture load among various Zr coping groups (p< 0.001) was determined. CONCLUSIONS: Novel Zr coping design for anterior PLZ crowns can provide better aesthetics with strength. Reducing the thickness of Zr coping in the aesthetic zone to 0.2 mm and providing a modified collar design (2.5 mm collar height on M, D, P, and 0.2 mm F) would provide strength without jeopardizing aesthetics.

Background The conventional susceptible-infectious-recovered (SIR) model tends to overestimate the transmission dynamics of infectious diseases and ends up with total infections and total immunized population exceeding the threshold required for control and eradication of infectious diseases. The study aims to overcome the limitation by allowing the transmission rate of infectious disease to decline along with the reducing risk of contact infection. Methods Two new SIR models were developed to mimic the declining transmission rate of infectious diseases at different stages of transmission. Model A mimicked the declining transmission rate along with the reducing risk of transmission following infection, while Model B mimicked the declining transmission rate following recovery. Then, the conventional SIR model, Model A and Model B were used to simulate an infectious disease with a basic reproduction number (r0) of 3.0 and a herd immunity threshold (HIT) of 0.667 with and without vaccination. The infectious disease was expected to be controlled or eradicated when the total immunized population either through infection or vaccination reached the level predicted by the HIT. Outcomes of simulations were assessed at the time when the total immunized population reached the level predicted by the HIT, and at the end of simulations. Findings All three models performed likewise at the beginning of the transmission when sizes of infectious and recovered were relatively small as compared with the population size. The infectious disease modelled using the conventional SIR model appeared completely out of control even when the HIT was achieved in all scenarios with and without vaccination. The infectious disease modelled using Model A appeared to be controlled at the level predicted by the HIT in all scenarios with and without vaccination. Model B projected the infectious disease to be controlled at the level predicted by the HIT only at high vaccination rates. At lower vaccination rates or without vaccination, the level at which the infectious disease was controlled cannot be accurately predicted by the HIT. Conclusion Transmission dynamics of infectious diseases with herd immunity can accurately be modelled by allowing the transmission rate of infectious disease to decline along with the combined risk of contact infection. Model B provides a more credible framework for modelling infectious diseases with herd immunity in a randomly mixed population.

The susceptible-infectious-removed (SIR) model offers the simplest framework to study transmission dynamics of COVID-19, however, it does not factor in its early depleting trend observed during a lockdown. We modified the SIR model to specifically simulate the early depleting transmission dynamics of COVID-19 to better predict its temporal trend in Malaysia. The classical SIR model was fitted to observed total (I total), active (I) and removed (R) cases of COVID-19 before lockdown to estimate the basic reproduction number. Next, the model was modified with a partial time-varying force of infection, given by a proportionally depleting transmission coefficient, $$\beta_{t}$$ β t and a fractional term, z. The modified SIR model was then fitted to observed data over 6 weeks during the lockdown. Model fitting and projection were validated using the mean absolute percent error (MAPE). The transmission dynamics of COVID-19 was interrupted immediately by the lockdown. The modified SIR model projected the depleting temporal trends with lowest MAPE for I total, followed by I, I daily and R. During lockdown, the dynamics of COVID-19 depleted at a rate of 4.7% each day with a decreased capacity of 40%. For 7-day and 14-day projections, the modified SIR model accurately predicted I total, I and R. The depleting transmission dynamics for COVID-19 during lockdown can be accurately captured by time-varying SIR model. Projection generated based on observed data is useful for future planning and control of COVID-19.

The risk of contact infection among susceptible individuals in a randomly mixed population can be reduced by the presence of immune individuals and this principle forms the fundamental of herd immunity. The conventional susceptible-infectious-recovered (SIR) model features an infection-induced herd immunity model, but does not include the reducing risk of contact infection among susceptible individuals in the transmission model, therefore tends to overestimate the transmission dynamics of infectious diseases. Here we show that the reducing risk of contact infection among susceptible individuals can be achieved by incorporating the proportion of susceptible individuals (model A) or the inverse of proportion of recovered individuals (model B) in the force of infection of the SIR model. We numerically simulated the conventional SIR model and both new SIR models A and B under the exact condition with a basic reproduction number of 3·0. Prior to the numerical simulation, the threshold for the eradication of infectious disease through herd immunity was expected to be 0·667 (66·7%) for all three models. All three models performed likewise at the initial stage of disease transmission. In the conventional SIR model, the infectious disease subsided when 94·0 % of the population had been infected and recovered, way above the expected threshold for eradication and control of the infectious disease. Both models A and B simulated the infectious disease to diminish when 66·7% and 75·6% of the population had been infected, showing herd immunity might protect more susceptible individuals from the infectious disease as compared to the projection generated by the conventional SIR. Our study shows that model A provides a better framework for modelling herd immunity through vaccination, while model B provides a better framework for modelling herd immunity through infection. Both models overcome the insufficiency of the conventional SIR model in attaining the effect of herd immunity in modelling outputs, which is important and relevant for modelling infectious disease, such as the COVID-19 in a randomly mixed population.

The risk of contact infection among susceptible individuals in a randomly mixed population can be reduced by the presence of immune individuals and this concept is referred to as herd immunity1–3. The conventional susceptible-infectious-recovered (SIR) model does not feature a reduced risk of susceptible individuals in the transmission dynamics of infectious disease, therefore violates the fundamental of herd immunity4. Here we show that the reduced risk of contact infection among susceptible individuals in the SIR model can be attained by incorporating the proportion of susceptible individuals (model A) or the inverse of proportion of recovered individuals (model B) in the force of infection of the SIR model. We simulated the conventional SIR model and both new SIR models under the exact condition with a basic reproduction ratio of 3.0 and an expected herd immunity threshold of 0.667 (66.7%). All three models performed likewise at the initial stage of an epidemic. In the conventional SIR model, the epidemic continued until 94.0 % of the population had been infected and recovered, way above the threshold for eradication and control of the epidemic. Both models A and B simulated the epidemic waning when 66.7% and 75.6% of the population had been infected, as a result of the herd effect. As a result, model A provides a better framework for modelling vaccine-induced herd or population immunity, while model B provides a better framework for modelling infection-induced herd or population immunity. Our results demonstrate how the new modelling framework overcomes the drawback of the conventional SIR model and attain the effect of herd immunity in modelling outputs, which is important for modelling infectious disease in a randomly mixed population, especially for the COVID-19 pandemic.