Tuesday, April 21, 2020

Where Will Herd Immunity From Coronavirus Allow Re-Opening?

Recent studies have shown that the novel coronavirus (SARS-CoV-2) may be far more infectious than previously thought, perhaps some 50 to 85 times more so (e.g., see https://www.cnn.com/2020/04/17/health/santa-clara-coronavirus-infections-study/index.html).  This evidently is due to the virus' ability to spread while infected persons are asymptomatic, with much of the spread apparently through aerial transmission.  The astonishing celerity of the infection rate means that areas of high infections may well be in the process of acquiring herd immunity.

Herd immunity is immunity of a large segment of a population to a disease agent, such as a virus.  When people become infected, they often produce antibodies that may then insulate them from further infection.  Antibodies don't always provide immunity, and if they do, it may last only a limited time.  But herd immunity, which is said to begin around the time when 50% or more of a population are immune, can stop or largely limit the spread of a disease before many of the non-immune people can be infected.  (In the same sense, high vaccination levels provide substantial protection to the non-vaccinated.)  Herd immunity tends to be most effective when immunity rates are 90% or higher, but lower levels can still be beneficial.

A region locked down by COVID-19 may be able to lift restrictions and stay open if it has herd immunity.  By contrast, a region without herd immunity that lifts restrictions sooner rather than later runs a potentially serious risk of the disease flaring up after people begin to mingle again.  A second and perhaps more rigid lockdown may have to be imposed to avoid tragic death rates.

Where is there herd immunity?  In the areas of greatest infection.  In America, that would be New York City.  Right now, NYC has about 140,000 confirmed cases.  Using 50 as a multiplier, that would imply that some 7 million New York City residents have been infected.  NYC has a population around 8.3 million.  If the large majority of the infected residents produced antibodies, and those antibodies provide immunity, then New York City is pretty likely to have herd immunity.  If that is the case, NYC might be able to re-open when other conditions for re-opening are met (such as clearing the case overload in its hospitals and acquiring enough antibody tests to verify its true infection rate).  It may be able to stay open because herd immunity would protect against re-infection and its economy may start humming again.

States where the levels of confirmed cases are much lower would also have numerous undiagnosed cases, but nowhere enough to acquire herd immunity.  Re-opening soon could involve a serious risk of a second lockdown and even more severe economic pain than they now feel.  Perhaps it's ironic, but the places that are feeling the greatest pain now from the novel coronavirus may be the places that  can re-open and prosper again the soonest.

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