COVID-19 Update from Dr. Smith: 4/21/20

Each day during the COVID-19 crisis, Dr. Craig Smith, Chair of the Department of Surgery, sends an update to faculty and staff about pandemic response and priorities. Stay up to date with us.

Dear Colleagues,

Allow me a brief segue through COVID science.  I have resolved some of my own confusion surrounding how the reproduction rate of a virus is measured.  R0 indicates how many other people one person will infect.  If R0 = 2, each infected person infects two others.  R0> 1 means infection will increase in the population, R0 < 1 means infection will decline.  Estimates of R0 for SARS-CoV-2 range from 2.2 to 5.7.  Measles ( R0 = 15-18) and Mumps (R0 = 10) are worse; anti-vaxxers take note.  R0 is also related to the percent of immunity required in the population to eliminate the disease (typically achieved through vaccination).  For SARS-CoV-2 that appears to be 80-90%.

Simplicity ends there.  R0 is not a rate.  It reveals nothing about how fast an infection spreads.  Worse, it is meant to apply only to a population in which everyone is susceptible, and in which no countermeasures have been taken to reduce spread.  Such fastidious assumptions are confusing and limit applicability. R, R, and Re are used to adapt the concept embodied in R0 to a real world of evolving immunity and countermeasures that change reproduction rate.  I’ll choose plain, simple “R.” Why does R matter? Notice that we could achieve R = 0 by immediately imprisoning the index case in a bell jar; no transmission, no epidemic.  Testing, contact tracing, social distancing, and PPE are all ways to decrease R. R < 1 is the goal of our collective countermeasures, at which point the epidemic recedes and eventually disappears.  Recedes and disappears…ay, therein lies the rub. When will the susceptible population be sparse enough, combined with countermeasures that don’t close the economy, to prevent R > 1? That is the 64-trillion-dollar question.  Among other things, we need widespread testing to help define the size of the susceptible population. Experts have guessed that 30-40% immunity may be all we need to hover below R = 1 while holding our breath for a vaccine. 

Now I will lurch from COVID science to the annals of adversity.  David Starr Jordan (1851-1931) was born on a farm in upstate New York.  His parents chose to have him attend the local high school for girls. After obtaining a BS from Cornell and an MD from Indiana Medical College, he pursued zoology, and became a renowned ichthyologist.  His signature accomplishment was a vast collection of preserved fish specimens. He was appointed President of Indiana University in 1885, where he lost his fish collection to a lightning fire. He painstakingly rebuilt his collection.  He was appointed the first President of Stanford University in 1891, where he lost most of his new collection in the 1906 earthquake. He declared “Man cannot be shaken and cannot be burned.” He rebuilt again. However great their importance to President Jordan, I realize that fish in formaldehyde are not patients on ventilators, but we are getting the chance to rebuild.  Just once, let’s hope, if we R right.

Craig R. Smith, MD
Chair, Department of Surgery
Surgeon-in-Chief, NYP/CUIMC

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