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countries by mid-April 2020. These predictions need to be interpreted with caution because of prediction intervals inherent to modelling, and because of the underlying assumptions of: 1) a stable diagnostic testing policy and capacity and 2) an absence of effective mitigation measures. 3 ECDC risk assessment Many unknowns remain regarding the virulence/pathogenicity, the effectiveness of different modes of transmission, the proportion of mild and asymptomatic cases, the infectivity during the incubation period and during recovery, the impact of individual or population-based preventive measures, the risk factors for severe illness besides age, and the effectiveness of treatment regimes. So far, detailed epidemiological data available are still limited. This assessment is based on facts known to ECDC at the time of publication, and unless otherwise stated, the assessment of risk refers to the risk that exists at the time of writing this report. It follows the ECDC rapid risk assessment methodology with relevant adaptations [53]. Risk assessment questions · What is the overall risk, as of 11 March 2020, associated with COVID-19 for the EU/EEA and UK? · What is the risk of sub-national community transmission occurring in countries in the EU/EEA and the UK in the coming weeks? · What is the probability of widespread national community transmission in the EU/EEA and the UK in the coming weeks? · What is the risk of healthcare system capacity being exceeded in the EU/EEA and the UK in the coming weeks? · What is the risk associated with transmission of COVID-19 in health and social care institutions with large vulnerable populations? What is the overall risk, as of 12 March 2020, associated with COVID-19 infection for the EU/EEA and UK? The risk of severe disease associated with COVID-19 infection for people in the EU/EEA and UK is currently considered moderate for the general population and high for older adults and individuals with chronic underlying conditions. In addition, the risk of milder disease, and the consequent impact on social and workrelated activity, is considered high. This assessment is based on the following factors: · There are an increasing number of cases in several EU/EEA countries without epidemiological links to explain the source of transmission. In some countries, transmission within healthcare settings has been reported affecting healthcare workers. As reported cases increase globally in a growing number of countries (found here), the likelihood of continued introductions into and between EU/EEA countries will increase. Given these factors, the probability of further transmission in the EU/EEA and the UK is considered very high. The speed with which COVID-19 can cause nationally incapacitating epidemics once transmission within the community is established indicates that it is likely that in a few weeks or even days, similar situations to those seen in China and Italy may be seen in other EU/EEA countries or the UK, as more countries report evidence of community transmission. · The evidence from analyses of cases to date is that COVID-19 infection causes mild disease (i.e. non-pneumonia or mild pneumonia) in about 80% of cases and most cases recover, 14% develop more severe disease and 6% experience critical illness. Severe illness and death is more common among the elderly and those with other chronic underlying conditions, with these risk groups accounting for the majority of severe disease and fatalities to date. In the event of a disruption of healthcare services, the impact could be very high. In addition to the public health impact with substantial fatal outcomes in high-risk groups, COVID-19 outbreaks can cause huge economic and societal disruptions. What is the risk of occurrence of subnational community transmission of COVID19 in the EU/EEA and the UK in the coming weeks? The risk of the occurrence of subnational community transmission of COVID-19 in the EU/EEA and the UK is currently considered very high. This assessment is based on the following factors: · Several events already reported in Europe indicate that local transmission may have resulted in several sub-national clusters. The accumulated evidence from clusters reported in the EU/EEA and the UK indicates that once imported, the virus causing COVID-19 can be transmitted rapidly. It is plausible that a proportion of transmissions occur from cases with mild symptoms that do not provoke healthcare-seeking behaviour. The increase in case numbers and the number of countries reporting those cases globally increases the potential routes of importation of the infection into and between countries in the EU/EEA and the UK. The likelihood of this occurring depends on the speed of detection of local transmission and whether effective response measures are applied early enough at-scale. Early evidence from several settings globally indicates that rigorous public health measures, particularly related to isolation and social distancing, implemented immediately after identifying cases can reduce but does not exclude the probability of further spread. · The impact of such clusters in local areas would be high, but would depend on national capacity to organise