Planning Parameters for COVID-19 Outbreak Scenarios Date: 2020-03-31 Expires: 2020-04-09 POCs: CDC Modeling Team: eocevent334@cdc.gov ASPR Modeling: How to Use this Document This document provides parameter values for five outbreak scenarios. These scenarios are to inform planning for potential widespread transmission of These scenarios are not predictions, nor are they meant to inform forecasts or estimates of the likely impact of COVID-19. Instead, the parameter values detailed below for the outbreak scenarios represent the professional and scientific judgments as values that would be appropriate to use for planning. Substantial scientific uncertainty remains around nearly all of these parameters. These values have expiration dates. Given the rapidly-changing state of the science surrounding the epidemiology of we expect to regularly update these estimates over time. If you need updated values, please request them through one of the POCs above. Outbreak Scenarios Below are parameter values for five outbreak scenarios to model for public health response, planning and preparation for the novel coronavirus outbreak. Each scenario has parameter values for the basic reproduction number (R0), case fatality ratio (CFR), proportion of infections that are relative infectiousness of individuals cases are 50% as infectious as cases) and the proportion of transmission that occurs prior to onset. At this time, there is little information on the effects of age on transmission and severity. As more data become available, these scenarios can be revised to reflect age effects. The first four scenarios were chosen to attempt to bound the likely potential outcomes. It is considered unlikely that any outbreak would be outside the range of these planning scenarios. The scenarios vary parameters related to transmission because these factors are judged to strongly influence the ability to identify and mitigate exposures. In this document, an individual should be taken to mean one who is either truly or else has such mild that they would not consider themselves ill. An example of the latter case is someone who retrospectively indicates that they did have mild back pain but did not think that it was indicative of illness. Values expire 2020-04-09. Scenarios are not predictions. The fifth planning scenario is a "best guess? of parameters based upon the current state of scientific knowledge, which is still highly uncertain. Because of the many unknowns, these values include much Subject Matter Expertise (SME) judgement and estimation. Higher parameters were selected because of: 1) the current state of knowledge and 2) to err on the side of caution as not over-estimate the ability of community mitigation to halt transmission. These scenarios are visualized by their relative severity transmissibility versus transmission fraction in Figure 1, below. A Will be constantly updated as new data are available Transmissibility and Severity Figure 1: Visualization of Scenarios Contribution Please note that modelers should not feel constrained by these suggested scenarios. You are free to use different parameters if you believe that they are more scientifically supported or more relevant to your particular scenario. Values expire 2020-04-09. Scenarios are not predictions. Table 1. Parameters values for 5 outbreak scenarios. Scenarios are not predictions, can?t inform estimates of likely impact, and are only appropriate to use for planning. Updates since prior version are in Red. Scenario 1: Scenario 2: Scenario 3: Scenario 4: Scenario 5: Moderate/high Moderate/ high High/very high High/Very high ?Best Guess? severity, low severity, high severity, low severity, high Source: SME Estimates Parameter contribution contribution contribution contribution Doubling Time Source: Preliminary ?7 Days Days "4.5 Days ?4.5 Days "5.5 Days estimatess Initial R0 Source2COVlD?19 estimates (Note that this does not necessarily 2 2 3 3 2.5 correspond to serologic attack rate in a homogenous- mixing SEIR model.) Overall Unmitigated Serologic Attack 50% 50% 70% 70% 60% ate Source: Model estimate from above parameters. 0?4: 0.006 0?4: 0.006 Case Fatah? 0?4: 0.04 0?4: 0.04 0?4: 0.01 Ratio 5?17: 0.004 5?17: 0.004 5?17: 0.03 5?17: 0.03 5?17: 0.0075 Source=C0V 019 18?49: 0.025 18?49: 0.025 estimates for overall; 50_64_0 075 50_64_0 075 18?49: 0.18 18?49: 0.18 18?49: 0.045 age-Speci?c assumed I to follow U.S. seasonal 65+: 1 65+: 1 65+_ 7 0 65+_ 7 0 65+. 1 75 distributb" Overall: 0.10? Overall: 0.10? Moderate estimates Overall: 1.0 Overall: 1.0 Overall: 0.25 were chosen to match 0'15 0'15 U.S. seasonal t. 0?4: 0.50 0?4: 0.50 0?4: 12.0 0?4: 12.0 0?4: 4.5 cm" 5?17: 0.1 5?17: 0.1 5?17: 1.5 5?17: 0.6 Hase ,t I, t, 18?49: 2.0 18?49: 2.0 18?49: 6.5 18?49: 6.5 18?49: 3.5 50?64: 4.5 50?64: 4.5 50?64: 10.0 50?64: 10.0 50?64: 7.0 5: . .) 65+: 4.5 65+: 4.5 65+: 17.0 65+: 17.0 65+: 10 urce: Preliminary covu)-19 estimates Overall: 4.0 Overall: 4.0 Overall: 8.0 Overall: 8.0 Overall: 5.5 Proportion of infections that are 20% 50% 20% 50% 35% Source: Preliminary estimates Relative infectiousness 50% 100% 50% 100% 100% of Values expire 2020-04-09. Scenarios are not predictions. individuals (among infections) Source: Assumption Proportion of transmission occurring prior to onset (among individuals) Source: Preliminary COVID-19 estimates 20% 40% 20% 40% 35% Pre-existing immunity Source: Assumption None Time to Onset days (mean) Source: estimates Average time between primary and secondary infection Source: Assumption from SARS days (mean) Table 2. Assumptions to help anticipate resource needs for COVID-19 outbreak scenarios Time to seek care (outpatient) Source: Survey of persons with ILI 52 days: 35% 3?7 days: 50% 28 days: 25% Mean time from onset to hospitalization (S.D.) 0?49: 5.00 (3.2) 50?64: 6.00 (3.6) Source: PreliminaryCOVlD?19 265: 5.0 (3.8) estimates Mean duration of 0?49; 3.3 (3.2) hospitalization (S.D) 50?64; 4.0 (3.3) :u:;;relimmary COVID 19 265: 5.1 (4.0 ICU among those 0?49; 10.0 hospitalized 50?64: 20.0 :uLcileellmmary COVID 19 65+. 300 ventilated among 0?49; 60.0 those in ICU 50?64: 75.0 Source: Preliminary COVID-19 65+. 750 estimates Median time from onset to death Source: Preliminary estimates all ages: 10 days Values expire 2020-04-09. Scenarios are not predictions. Table 3. Key transmissibility and severity parameters for seasonal influenza. Parameter Seasonal in?uenza Basic Reproduction Number (R0) 13 Source: 0?4: 0.006 5?17: 0.004 18?49: 0.025 65+: 1 Approximate Case Fatality Ratio overall: 040?045 Source: CDC seasonal in?uenza burden estimates 0?4: 0.70 5?17: 0.25 18?49: 0.50 Approximate Case Hospitalization 50?64: 1'00 Ratio (CHR) 55+: 9-0 Source: CDC seasonal in?uenza burden estimates Overall: 1.5 Values expire 2020-04-09. Scenarios are not predictions.