Readers are invited to submit letters for publication in this department. Submit letters online at http://joem.edmgr.com. Choose "Submit New Manuscript." A signed copyright assignment and financial disclosure form must be submitted with the letter. Form available at www.joem.org under Author and Reviewer information. To the Editor: Persons with ≥65 years of age, or those with chronic conditions, such as type 2 diabetes, hypertension, dyslipidemia, and obesity (BMI > 30), have faced increased mortality from COVID-19.1 For example, people with type 2 diabetes have a 3 times greater risk of death than the general cohort. These data suggest that the fatality rate may be close to 10% for people with type 2 diabetes, and in persons with 65 years old or older comparing with people under 50 years without high-risk chronic conditions, this probability increases more than 20 times. Besides, others clinical conditions may increase morbidity and mortality, for instance, kidney disease, immunocompromised, and sickle cell patients. Similarly, others conditions have described as a possible high or medium-risk categories, such as patients with chronic neurologic disorders, liver disease, pregnancy, type 1 diabetes, smokers, thalassemia, cerebrovascular disease, and asthma.2–5 In this context, other reports have described that of hospitalized adult patients, 89.3% had one or more underlying conditions; the most common were hypertension (49.7%), obesity (48.3%), chronic lung disease (34.6%), diabetes mellitus (28.3%), and cardiovascular disease (27.8%).6 Some studies, in which the viability and stability of SARS-CoV-2 have been evaluated in aerosols and on various surfaces, show that the virus remains viable in different materials (up to 72 h for plastic materials, 48 to 72 h for stainless steel, up to 24 h for cardboard, and around 4 h for copper). Thus, the use of massive public transport systems characterized by enclosed public spaces, for instance, buses, trains, and trams, may increase the risk of contagion due to presence of plastic and stainless steel materials.7 In addition, this kind of transport is characterized by being closed spaces and with a massive influx of people. In this way, some studies have reported that the SARS-CoV-2 can be kept in the air in closed buses without ventilation for at least 30 minutes without losing infectivity, and that it is likely that small particles can diffuse indoors over distances of up to 10 m.8 Also, some findings suggest that the potential for virus transmission may persist for hours or days in indoor environments. In this context, understanding the factors that contribute to the persistence of SARS-CoV-2 on surfaces and indoors environments could allow a more accurate estimate of the risk of contact transmission.9 The World Health Organization and governments have recommended maintaining a social distance of 1.5 or 2 m (6 feet) from each other in order to minimize the risk of contagion through droplets. However, recently published studies support the hypothesis of virus transmission at a distance of 2 m from an infected person.9 A meta-analysis of observational studies shows the best evidence currently available, which suggests a significant decrease in the probability of contagion, due to decreased spread of the virus, if these recommendations are followed.10 The United States is proposing to reduce the density of people in the workplace to decrease the risk of transmission, segmenting work schedules, alternating work presence, and promoting continuous remote work schedules. Some strategies, such as alternating work shifts, including schedules in the morning and the night shifts, reduce density in the workplace and contribute to reducing the use of public transport during peak hours, which reduces the risk during commuting. However, despite the recommendations of prevention and control bodies, the prevention policies present some implementation limitations. In Colombia, similar to other countries, the Ministry of Education according to the guidelines for the management of the emergency by COVID-19 defined provision of the education service using the alternation strategy (a combination of academic work at home assisted by virtual tools, with periodic face-to-face meetings and integration of pedagogical resources). We also recommend public health organizations to coordinate with education institutions in adapting biosecurity protocols to the specific conditions of each initiation and in compliance with the regions public health needs. These recommendations would be implemented in the short and medium-term to allow the students to return to educational institutions and to reduce the risk of the spread of the virus. Therefore, for the progressive return to universities and colleges, using the alternation strategy, a proposed of risk of morbidity or mortality by COVID-19 for persons in educational institutions could help to identify "low risk" individuals who can return to in-person activities, and those at "high risk" for teleworking and tele-education. We propose a risk score for educational institutions to preliminarily determine if students, professors, and administrative support staff should return to the classroom or continue with virtual educational activities (student and professors) or by telework/remote work (administrative support staff). The proposed risk score for persons in educational institutions is based on the probability of contagion, determinate by the risk of the occupational exposure and type of transportation, as well as the probability of more severe COVID-19 illness outcomes and mortality, determinate by age and comorbidities of the persons.FIGURE 1: Proposed risk stratification for persons in educational institutions. Morbidity/mortality Risk: High 3, medium 2, and low 1. Transmission risk: High 3, medium 2, and low 1. Type of transportation: Public 2 and private 1.CLASSIFICATION OF OCCUPATIONAL EXPOSURE RISK (EXPOSURE RISK SETTING) TO SARS-COV-2 High OccupationalExposure Risk: Persons with high potential for exposure risk setting to known sources of COVID-19, or people in areas with outbreaks.11,12 Medium OccupationalExposure Risk: Persons who require frequent or close contact for exposure risk setting (ie, <2 m away) with people who may be infected with SARS-CoV-2 but are not known COVID-19 patients.11,12 Low OccupationalExposure Risk: Persons who do not require contact with people known or suspected to be infected with SARS-CoV-2, or frequent close contact for exposure risk setting (ie, <2 m away) from the public.11,12 CLASSIFICATION ACCORDING TO THE TYPE OF TRANSPORTATION Public transport system: Includes travel to workplaces using mass public transport systems, such as buses and the metro system (trains, trams, etc.). Private transportation system: Includes traveling to workplaces by car, motorcycle, bicycle, or walking. CLASSIFICATION ACCORDING TO THE RISK OF MORBIDITY AND DEATH (MORE SEVERE COVID-19 ILLNESS OUTCOMES AND MORTALITY) FROM COVID-19 According to age and presence of high-risk conditions (hypertension, obesity, chronic lung disease, diabetes mellitus, and cardiovascular disease)1–5: High risk: Advanced age (65 yrs or more) or median (50 to 64 yrs) age with high-risk conditions. Medium risk: Middle age (50 to 64 yrs) or youth (18 to 49 yrs) with high-risk conditions. Low risk: Younger age (18 to 49 yrs) without high-risk conditions. FIGURES ALLOCATION AND RISK SCORE METHODOLOGY Two variables were established that measure the probability of contagion and one that measures the probability of morbidity and death: Morbidity/mortality Risk: High 3, medium 2, low 1. Transmission risk: High 3, medium 2, low 1. Kind of Transport: Public 2, private 1. The aggregate of the variables of "transmission," "morbidity/mortality," and "transport" figures define both the result of the "risk score" and the degree of risk (high, medium, and low): Values 4: classification A. Low risk of morbidity/mortality for Exposure suspect from COVID 19. Values between 5 and 6: classification B. Medium risk of morbidity/mortality for Exposure suspect from COVID 19. Values between 7 and 8: classification C. High risk of morbidity/mortality for Exposure suspect from COVID 19. RECOMMENDATIONS ACCORDING TO CATEGORIES A. Being present. Besides, use facemasks outside the home, continuously carry out hand hygiene (Figure 1). B. Consider virtual study and teleworking. Besides, assess individual risks, opportunities to mitigate exposure, and in addition to the recommendations outlined in A (Figure 1). C. Perform only telework or virtual study. Besides to the recommendations described in A (Figure 1). There is a need to define a protocol for assistance and gradual reactivation of educational activities, according to the risk of morbidity/mortality and the probability of contagion, proposing strategies that minimize the risk. In this context, the risk score suggested for persons in educational institutions may be useful. So, for persons (professors, administrative support staff, and students) classified in categories A and B, the institution may implement a combination of work academic at home (with the support of virtual education strategies), complemented by periodic face-to-face meetings and integration resources. Also, assistance to the educational institution would be according to compliance with biosecurity protocols, and the specific condition of each educational institution. Among the suggested recommendations to identify the population at the highest risk, it may be necessary to implement different strategies, such as the identification and characterization of the educational community, and the development of public health surveillance systems, mainly in epidemiological outbreaks. Besides, establish specific measures for teaching and administrative staff over 65 years of age and staff with pre-existing morbidities. Also, it needs to implement strategies to periodically review the health status of students, professors, and administrative and service personnel who participate in face-to-face activities. Without the availability of both a safe and effective vaccine or treatments for COVID-19, the peaks of outbreaks may cause a high number of patients requiring hospital admission, and saturating the capacity of the health systems. In this context, there is need to identify and implement interventions to mitigate the spread, including the increased testing, and reinforcing biosecurity recommendations. These considerations are oriented to those gradually restarting their work and social activities, among them, the return to educational institutions. The proposed risk score for persons in educational institutions is a starting point to help decision-makers in this kind of institutions in the world for establishing in which cases professors, administrative support staff, and students will be able to start attending institutions, or conversely, in which cases continue through virtual tools education and telework. The risk level depends on the contact within 2 m of people known or suspected infected with SARS-CoV-2, or the requirement for repeated or prolonged contact with people known suspected of being infected. Besides, it is essential to take into account regional infection rates by geographical areas as reported by governments, for the consideration of the occupational and educational system. LIMITATIONS OF THE RISK SCORE FOR PERSONS IN EDUCATIONAL INSTITUTIONS Due limitations to this proposed risk score for individuals at educational institutions, and lack of prospective study it should be considered preliminary and used with caution. First, it is important to denote that a complete description of the degree of the risk: high, medium, and low, or high and medium, for transmission risk or type of transportation, respectively, is not yet known. Furthermore, more research is needed to better understand the significance of these variables and situations that can affect the risk community and occupational transmission of COVID-19. Second, other socioeconomic variables may affect the risk, such as income, community safety, and social supports; so, the inclusion of these variables could improve the precision to assess the risk score for persons in educational institution. However, in an indirect approach, the type of transportation variable could reflect some of these socioeconomic variables. Moreover, third, this proposed risk score assumes equal weight to each of the factors, and this condition could be affected and changed with more data and information generated from more research. We propose the study of risk score for persons in educational institutions to assess its accuracy and utility and adapted as more information arises. In the meanwhile, institutions can consider how similar risk stratification may help mitigate community and occupational spread of COVID-19.