We propose a new compartmental mathematical model describing the transmission and the spreading of COVID-19 epidemic with a special focus on the non-total immunity. The model (called SIARD) is given by a system of differential equations which model the interactions between five populations “susceptible”, “reported infectious”, “unreported infectious”, “recovered with/without non total immunity” and “death”. Depending on the basic reproduction number, we prove that the total immunity induces local stability-instability of equilibria and the epidemic may disappear after a first epidemic wave and more epidemic waves may appear in the case of non-total immunity. Using the sensitivity analysis we identify the most sensitive parameters. Numerical simulations are carried out to illustrate our theoretical results. As an application, we found that our model fits well the Moroccan epidemic wave, and predicts more than one wave for French case.

Working with visual display terminals (VDT) is growing significantly in the global information age, with the vast growth of digital devices, which is also followed by a higher incidence of health issues. To explore the physical and mental health impacts of long term use of visual display terminals on the population in Jeddah, Saudi Arabia. It was a cross sectional study; the method of non-probability convenient sampling was used to collect data on 503 subjects, in Jeddah city through online-Google forms. Data collection was done through the use of a predesigned questionnaire that provided information on individual, sociodemographic, and clinical features of the subjects as well as information on the aspects of use of VDT. Statistical analysis: data analysis was performed in SPSS version 23. The sample size was 503 subjects with mean age of 31.95 ±12.51 years, 98% of them used VDTs. They used it almost every day (mean= 6.6 ± 1 days), for about 8 hours per day (mean= 8.2± 4.1 hours). Students and office employees used the VDT > 7 hours/day. Almost, all the subjects (99%) used smart phones. Headache, neck pain and shoulder pain, lower back pain, dryness of the eye and interrupted sleep were common complaints among VDT users. It also, interfered with their daily life activities. In principal component factor analysis, duration of use of VDT in hours/day (weight = 0.710), and days/week (weight = 0.724) were significantly loaded on one factor; however, no other variables had weight greater than 0.3 on this factor.