Writing in the Times,
David Rubin and Paul Offit describe a Pandemic model they have developed and applied to data from 46 US states. The exercise, they say
revealed that crowding and population density, whether in densely populated areas in New York City or a meatpacking plant in South Dakota, are the most important factor in determining the havoc the virus can wreak.
After accounting for age distribution and health issues it was clear that risk not only of infection but of death broke between two groups: those in densely crowded areas, and everyone else. Large, densely populated areas like New York and Chicago had nearly twice the rate of transmission in the first two weeks of their outbreaks than the least densely populated areas we are tracking, like Birmingham, Ala., or the metro area of Portland, Ore. Yes, we did find that warming spring temperatures in some areas are helping to reduce transmission, but that effect is dwarfed by the impact of population density in our largest cities, particularly in the North.
Re-opening Philadelphia, they argue, would be disastrous, but in Harrisburg the virus would probably "fizzle out" if some basic safety measures are retained.
This means that areas in the country that are less densely populated or are already benefiting from warmer spring temperatures will probably be able to reopen more quickly, as long as the number of cases in their area have sharply reduced — we can’t give an exact rate — and if they maintain workplace safety, moderate distancing, and test to identify and trace outbreaks early.
Large, densely populated cities are going to need a more cautious plan. This is not just because more crowded areas increase the risk of spread, but also because we’re learning that crowding itself may also affect the death rate. The relationship between the amount of virus to which one is initially exposed and the severity of the illness is found in most infectious diseases. Models assessing outcomes from the 1918 Spanish flu epidemic reveal that the likelihood of death was dependent upon the number of infected individuals with whom that person came into contact. When a family is infected by chickenpox, the second child to contract the virus often becomes more seriously ill, presumably because they have been exposed to more of the virus.
"Re-opening" is going to be a slow and partial thing no matter what governments decide; anybody out there really want to attend a movie in a crowded theater right now? My office is in Washington, DC, and whatever my bosses say I'm not going back until I've been vaccinated.
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