New (4/19/20) Scenarios based on Santa Clara County data

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New (4/19/20) Scenarios based on Santa Clara County data

Post by KenHess »

On April 17, 2020, Bendavid et al published "COVID-19 Antibody Seroprevalence in Santa Clara County, California" in medRxiv. This study of 3,330 people showed much higher rates of asymptomatic infection (approximately 48 asymptomatic cases for every symptomatic one) than previous estimates. One of the authors, Andrew Bogan, also had an op-ed piece in the April 17, 2020, Wall Street Journal, "New Data Suggest the Coronavirus Isn’t as Deadly as We Thought."

In SimPandemic, asymptomatic cases are specified in Custom Settings - Chance of Being Asymptomatic (percentage). The original SimPandemic Scenarios were all set to 25% asymptomatic, the center of estimates as of a week ago. The Santa Clara County data suggests that the parameter should be at least (48,000 – 1,000)/48,000 = 98%, showing how quickly and how dramatically our understanding of the virus is changing.

We have added two new Scenarios that both have Chance of Being Asymptomatic set to 98%:
- (New! 4/19/20) Runaway COVID-19 outbreak with 98% of cases asymptomatic
- (New! 4/19/20) Possible Solution #2A: Strong social distancing, followed by weak (except the elderly), followed by a vaccine

For both new scenarios, the total number of deaths is dramatically lower than the original Scenarios that they were based on. For Possible Solution #2A, we also reduced the severity of business closures (see the form at Custom Settings - Social Distancing & Business Closures). Fewer deaths and fewer business closures has a very positive impact on Economic Output. The Santa Clara County data is very good news and it will have a tremendous impact on what strategies make sense going forward.

If this research is validated in other communities (and we expect it will), we will update all scenarios.

NOTE: The current version of SimPandemic has an input at Custom Settings – Disease Characteristics for Chance of Death (percentage of symptomatic cases). "Percentage of Symptomatic Cases" is the key phrase. It means that we use the same death rate even though the number of infected individuals is now known to be much higher. This is the first time that we have had data for Chance of Death (percentage of infected cases). In a future release we will add an option to input either percentage, depending on what the user has. For now, you must input Chance of Death (percentage of symptomatic cases), a number that will be much higher than the numbers discussed in the above articles.


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