COVID-19 Modeling Update: May 15, 2020

COVID-19 Modeling Update: May 15, 2020

Friday, May 15, 2020 | by Alex Hartzman, Al Dobson, Joan DaVanzo

Tags: COVID-19

Federal guidance has shifted to reopening and states are just beginning to lift restrictions. With no vaccine in the foreseeable future and testing still inadequate (both for active disease and presence of antibodies), many models indicate that the U.S. is poised for major resurgences in infections in the coming months. These secondary spikes in infection may be more devastating than the first for many localities, depending on:

  • How hard they were hit the first time (and thus whether some amount of herd immunity exists);
  • How many active infections are present in the population; and
  • How much people start mixing as restrictions are eased, combined with local population density considerations

As in the 1918 influenza pandemic, localities have reacted differently to the pandemic at hand – states and municipalities have closed to different degrees at different response speeds and are now relaxing those restrictions differentially as well. In 1918, this led to different cities having very different outcomes when it came to both initial and resurgent peaks – both in terms of infections and in longer range economic terms.

What do we know about these factors? First, estimating the portion of the population that has been infected at this point is impossible without major increases in serological sampling to detect antibodies. We can make a rough estimate from apparent U.S. deaths (over 86,000 as of today’s writing) and an assumed death rate (let’s call it 0.42%). Thus, we estimate around 20M or 6% of the U.S. population has been infected (as of about two-three weeks ago considering deaths lag infection onset) is far lower than what it would take to achieve herd immunity (70-90% infected). This means that many areas have a large susceptible population that has not yet been exposed to the disease, both in pockets within emerging hotspots but also as many major population centers that have not yet experienced massive outbreaks.

Second, without much expanded testing and systematic contact tracing, we will not know who is currently infected and who is still susceptible. The disease is spread when these populations mix. Understanding who is infectious and keeping them isolated from susceptible persons (particularly high-risk groups) is imperative.

Third, as governors have eased restrictions, populations have initially proved wary to return to pre-pandemic normality. This is understandable given the dangers still posed to the general population but may not last. There will be increasing political and social pressure to “reopen” the economy, but so far the safeguards and careful evaluation not been conducted – neither individual nor population safety is guaranteed.

At this point the federal government is encouraging an informative and potentially devastating national experiment. Some communities have heeded the lessons of 1918 so far, and some have not. As a country, are we repeating the same errors and making worse ones despite a century of scientific advances and decades of disaster preparation?


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