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and clinical information on the cases of COVID-19 identified so far (e.g. efficiency of different modes of transmission, proportion of mild and asymptomatic cases, transmission during incubation and recovery period, effectiveness of treatment regimes, risk factors for severe illness besides age, effective preventive measures). Given these limitations, ECDC will revise the current risk assessment as soon as more information becomes available. 8 Source and date of request ECDC internal decision, 9 March 2020. 9 Consulted experts ECDC experts (in alphabetic order): Cornelia Adlhoch, Leonidas Alexakis, Agoritsa Baka, Eeva Broberg, Sergio Brusin, Julien Beaute, Nick Bundle, Mike Catchpole, Orlando Cenciarelli, Scott Chiossi, Edoardo Colzani, Angelo D'Ambrosio, Stefania De Angelis, Dragoslav Domanovic, Erika Duffell, Margot Einöder-Moreno, Emilie Finch, Joana Gomes Dias, Silvia Funke, Josep Jansa, Helen Johnson, Tommi Karki, John Kinsman, Vicky Lefevre, Katrin Leitmeyer, Felix Lotsch, Angeliki Melidou, Thomas Mollet, Otilia Mårdh, Lina Nerlander, Teymur Noori, Daniel Palm, Pasi Penttinen, Anastasia Pharris, Diamantis Plachouras, Emmanuel Robesyn, Senia Rosales-Klintz, Andreea Salajan, Gianfranco Spiteri, Carl Suetens. 10 Disclaimer ECDC issues this risk assessment document based on an internal decision and in accordance with Article 10 of Decision No 1082/13/EC and Article 7(1) of Regulation (EC) No 851/2004 establishing a European centre for disease prevention and control (ECDC). In the framework of ECDC’s mandate, the specific purpose of an ECDC risk assessment is to present different options on a certain matter. The responsibility on the choice of which option to pursue and which actions to take, including the adoption of mandatory rules or guidelines, lies exclusively with the EU/EEA Member States. In its activities, ECDC strives to ensure its independence, high scientific quality, transparency and efficiency. This report was written with the coordination and assistance of an Internal Response Team at the European Centre for Disease Prevention and Control. All data published in this risk assessment are correct to the best of our knowledge at the time of publication. Maps and figures published do not represent a statement on the part of ECDC or its partners on the legal or border status of the countries and territories shown. Annex 1. Scenarios to describe progression of COVID-19 outbreaks The following five scenarios, adapted from ECDC’s strategic analysis, are used to describe the possible progression of the COVID-19 outbreak in EU/EEA countries. Scenario 0 describes a situation with no reported cases in the country and multiple introductions and/or community transmission elsewhere in Europe. At this stage, the main objective for public health measures should be to enable rapid detection and isolation of individual cases to prevent domestic transmission chains, and to prepare for the response once cases are detected in the country. Scenario 1 describes a situation with multiple introductions but limited local transmission in the country. Despite the introductions there is no apparent sustained transmission (only second generation cases observed or transmission within sporadic contained clusters with known epidemiological links). In this situation, the objective is containment of the outbreak by blocking transmission opportunities, through early detection of imported and locally-transmitted COVID-19 cases in order to try to avoid or at least delay the spread of infection and the associated burden on healthcare systems. Delaying the start of local transmission will allow the current influenza season to end, freeing up some healthcare capacity. Scenario 2 describes a situation with increasing number of introductions and of more widespread reports of localised human-to-human transmission in the country (more than two generations of cases outside of sporadic clusters with known epidemiological links). In this situation, the objective remains to contain where practicable and otherwise slow down the transmission of the infection. This will increase the time available for development, production and distribution of PPE and effective therapeutic options, and would play a crucial role in reducing the burden on the healthcare system and other sectors, particularly if wider transmission of COVID-19 is delayed beyond the ongoing influenza season. A reduced burden would also allow for more time to increase laboratory capacity, and increase surge capacity in healthcare services. All these measures will facilitate effective treatment of infected patients [44]. Rapid collection and analysis of epidemiological and virological data will enable targeting of measures in this scenario and later. Scenario 3 describes a situation with localised outbreaks, which start to merge becoming indistinct. In this scenario, there is sustained human-to-human transmission in the country (more than two generations of cases outside of sporadic clusters with known epidemiological links) and an increasing pressure on healthcare systems. The objective at this stage is to mitigate the impact of the outbreak by decreasing the burden on healthcare systems and protect populations at risk of severe disease. At the same time, operational research should guide developing better and more efficient diagnostic and