The coronavirus outbreak continues its relentless spread from population centers on the coasts to the center of the country, even as newly reported cases overall decline.
As the three figures below indicate, the number of new cases in the United States has dropped from a peak of 32,000 per day on April 10 to 24,000 per day on May 14.
We project that total U.S. coronavirus cases will approach 1.5 million by the end of the week.
Our projections for the spread of the disease are for total U.S. cases to approach 1.5 million by the end of the week. Based on those projections, and given the current mortality rate of 6.0%, we expect the U.S. death toll to approach 90,000 by the end of the week.
Our death projection is based on the latest mortality rate, which we have extrapolated with no prior knowledge of the course of treatments now available.
But that the mortality rate has doubled from less than 3% at the start of April to 6% a month later is distressing and may speak to the distance of current patients to health care providers. It also could be attributed to the overwhelming flood of patients at community hospitals or to the existence of pre-existing conditions of current patients.
This leads us to a discussion of modeling the spread of the virus inland and away from the two points of origin, on the East and West Coasts.
The standard epidemiology model consists of solving a series of differential equations given assumptions of the rate of infection, the containment policy and the rate of recovery. Those assumptions can and have changed over time as new data becomes available.
While the spread of the virus in the major metropolitan areas has been decelerating, it has been trending higher in all other states.
We’ve seen the rate of infection varying according to population density, work conditions, social conventions and traits ranging from age to ethnicity.
The containment policy refers to the adoption of social distancing by the public and as mandated by the government. During this pandemic, U.S. policy has ranged from denial, to the shutdown of all interaction, to refuting the existing rules of interaction. Now, several states are in the process of reopening their economies and restoring social interaction.
The rate of recovery includes an immunity component that would allow formerly infected people to re-enter the public sphere without fear of infecting those with no immunity — either because the susceptible people haven’t been exposed to the virus or because they cannot tolerate the vaccination. (This is referred to as “herd” immunity, which we’ll get back to in our brief discussion of Sweden.)
Dividing the states by density and political characteristics draws some immediate conclusions about the need for multiple models.
We have divided the states into two groups: The six states that have suffered 50,000 or more coronavirus cases, which we’ll call the major states, including (in order) New York, New Jersey, Illinois, Massachusetts, California and Pennsylvania; and all other states.
While the spread of the virus in the major metropolitan areas has been decelerating since early April, it has been trending higher in all other states. Note that the number of newly reported infections in all other states are nearly 13,000 per day, which compares to the 10,000 infections per day in the six major states.
The experience with the staggering spread of the virus in the metropolitan areas should highlight the importance of social distancing; its effectiveness in limiting the spread should provide guidance to policymakers and the public at large.
A brief look at Sweden
Then there is Sweden, which has taken an altogether different approach to the virus, one of keeping the economy open as much as possible. Senator Rand Paul, a Republican from Kentucky, praised its approach to the pandemic this week during a Senate committee hearing.
Sweden has opted for selected closures. The goal is to achieve herd immunity.
Put simply, Sweden has opted for selected closures. The goal is to achieve herd immunity. But this assumes that immunity exists and can be transmitted by social interaction.
The argument against that policy is that there are too many unknowns to risk allowing children back in school or — at the polar opposite – the complete reopening of non-essential businesses and the re-opening of social gatherings.
In the meantime, the number of newly reported cases in Sweden shown in the first figure below looks more like the experience in the all-other-states category than in the deceleration of cases in the major states category.
In the second figure, the accumulated number of cases in Sweden is slowing but remains on an exponential growth path.
The third figure shows that daily deaths have been inconsistent, though with a mortality rate of 12%, that is twice the U.S. mortality rate. This strongly implies that the Swedish policy option is a nonstarter in the U.S.