Oregon is one of the states with the lowest per capita COVID-19 infection rates. However, despite our best efforts, we are still seeing about 50 new cases per day (down only a little from a high of about 70 cases per day five weeks ago). Nothing much has changed for the last two or three weeks. Oregon’s story is just a milder version of what is happening in the rest of the nation. Let’s look at the data and see what it all means.
Update on South Dakota
It has been a couple of weeks since I last looked at the trajectory of our pandemic. South Dakota now seems to understand the seriousness of their outbreak, and they are on track with the growth rate of the rest of the country. The infection rate of the virus has been shown to be reduced when isolation and social distancing are put into effect. In South Dakota, the Smithfield meat packing plant in Sioux Falls employed 4,000 people working in close proximity. When the plant was closed on April 15, it accounted for more than half of the state’s COVID cases. Cleaning up that single hot spot dramatically changed the trajectory of the exponential growth that had gripped the rural state.
Meanwhile, nothing much has changed in Oregon. Like much of the rest of the country, daily case numbers have come off their highs, but have stubbornly refused to decline much further.
The South Dakota case illustrates how important “hot spots” are for spreading the disease. On the national level, we see today there are still hot spots in the Northeast as well as many localized hot spots in states in the Midwest, many due to exposure in meat packing facilities.
New York Case Rates
The one place in the country where there really does seem to be progress is New York. Almost a third of the cases in the nation have been in the New York metropolitan area. Like the Smithfield meat plant in South Dakota, New York City is a hot spot that drives and distorts the entire nation’s statistics. At this point, cases in New York City are falling. A new tool from Covid Act Now lets you see the data on a local level.
The daily new case rate has been slowly dropping since the middle of April. The COVID Act Now Model allows you to examine averaged state numbers, or you can drill down to the county level to see what is happening on the local level. If you poke around the COVID Act Now map, you will discover that there are a few states with an infection growth rate below one, a few near one, and half of the states where the infection is still growing strongly (with an infection growth rate greater than one). States with growth rates less than one include many of the early hard-hit states such as CA, WA, NY, NJ, MI, CT, and LA.
The dimensionless growth rate can be interpreted as the average number of people that become infected from a single infectious person. For the COVID-19 pandemic, the intrinsic growth rate, R0 , is about 3 for a naive population without social distancing or extraordinary sanitation measures. A single infected person manages to infect about three others before recovering or dying. Despite our best efforts at social distancing and washing our hands going on for several weeks now, it is clear from the range of outcomes coming from states with a variety of policies, that we are stuck pretty close to a growth rate near one across the nation. This has resulted in a long plateau in the new case rate. Nearly 30,000 new cases a day in the U.S. accompanied by almost 2000 deaths a day has become normal for the past four weeks.
One thing that will reduce the growth rate is if a certain percentage of the people interacting with the infected person are immune to infection. We finally have some data on actual population-wide infection rates coming from antibody testing in New York State. The survey found that about 20% of residents in New York City have antibodies from the COVID infection. In Long Island and nearby suburbs, about 12% have had the disease, whereas in upstate and western New York the average immune population is closer to 3%.
The immune fraction of the population in New York City is certainly a factor in containment of the infection at this point. Without 20% of the population immune to infection, the growth rate would be about 20% higher. Instead of being below one with contracting case numbers, we would still be seeing evermore new cases. If you look at upstate New York, the counties around the state capital in Albany have COVID Act Now growth rates around 1.2 where the antibody rate is only 3% of the population. These regions of the state would be closer to containment if the people there had the immunity of the city dwellers.
Most of the nation is still doing its best to isolate and limit the spread of the disease. These efforts seem to offer nothing better than a growth rate near one. It appears that mandated, but largely voluntary, behavior modifications to control the pandemic are insufficient. American culture, with its strong component of individualism, combined with political division and contradictory messaging, seem likely to weaken whatever cohesive social isolation we have imposed upon ourselves. When that happens, case numbers will grow, but the consequences will not be felt for yet another month. Without removing infectious cases expeditiously before they have an opportunity to infect others (contact tracing and quarantine), we are doomed to wait for herd immunity to slow the spread. We can see herd immunity helping now in New York City, but at a tragic cost.
There is a lot of talk about “re-opening” the economy. Not a good plan, from what I can see, until we have yet another mechanism in place that further reduces the effective growth rate. Any relaxation of restrictions or weariness on the individual level will result in growing case numbers again, and we will have lost what little containment we have achieved.