How Covid-19 Spreads. The Effect Of Lockdowns.

Here's a chart of the new COVID cases in the various states relative to the population over the past 7 days. The darker the color, the greater the number. The geographic distribution is striking. The history of the virus activity since March is one of moving from one area of the country to another, first the Northeast, then the South and West, and now the Mid-West and Mountain states. The only exception is New Mexico which initially escaped the involvement in the Southwest, but now has more intense infection.

What explains this? Why, as the virus spreads from one area to the next, doesn't it simply persist and grow worse in the new site. Why does it appear to die away and move on? I like the explanation that in every community there is variation in susceptibility so that when it enters there is a large outbreak followed by a dying down as the virus encounters more resistant individuals. To be sure this is the usual behavior of epidemic illnesses. There is considerable scientific justification for this idea. It's becoming increasingly clear from studies of T cell reactivity to the virus that resistance is much more prevalent than previously thought and may be seen even before any possible previous exposure, perhaps from contact with other common coronaviruses. T cells are recruited against the virus invaders early on, often before antibodies appear and probably confer much longer lasting immunity than is suggested by antibody presence. Some of this might begin to explain the puzzling low incidence of infection in children and the likelihood of only mild symptoms in younger individuals.

This new understanding suggests that lockdowns in rapidly worsening areas may be necessary early on to prevent overwhelming of the medical facilities, but if continued beyond that may be a setup for recurrences. As social interaction resumes the virus encounters individuals previously unexposed and susceptible and surges, as we saw recently happening in Europe and some Northeastern states. Consistent with this idea is that cases now seem to be leveling off or declining in most of these areas. Considering all of this, as some experts contend, should our public health strategy be to concentrate our preventive efforts and vaccine administration when available to those at high risk and otherwise allow more general immunity to develop, and at the same time avoiding the many serious consequences of intense societal lockdowns.

 

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