Wednesday, May 20, 2020

The Unspoken Goal Has Always Been Herd Immunity


project-syndicate |  Science cannot determine what the correct COVID-19 response should have been for each country. A model may be considered validated if its predictions correspond to outcomes in real life. But in epidemiology, we can have confidence that this will happen only if a virus with known properties is allowed to run its natural course in a given population, or if there is a single intervention like a vaccine, the results of which can be accurately predicted.

Too many variables – including, say, medical capacity or cultural characteristics – scrambles the model, and it starts spewing out scenarios and predictions like a demented robot. Today, epidemiologists cannot tell us what the effects of the current COVID-19 policy mix will be. “We will know only in a year or so,” they say.

The outcome will therefore depend on politics. And the politics of COVID-19 are clear enough: governments could not risk the natural spread of infection, and thought it too complicated or politically fraught to try to isolate only those most at risk of severe illness or death, namely the 15-20% of the population aged over 65.

The default policy response has been to slow the spread of natural immunity until a vaccine can be developed. What “flattening the curve” really means is spacing out the number of expected deaths over a period long enough for medical facilities to cope and a vaccine to kick in.

But this strategy has a terrible weakness: governments cannot keep their populations locked down until a vaccine arrives. Apart from anything else, the economic cost would be unthinkable. So, they have to ease the lockdown gradually.

Doing this, however, lifts the cap on non-exposure gained from the lockdown. That is why no government has an explicit exit strategy: what political leaders call the “controlled easing” of lockdowns actually means controlled progress toward herd immunity.

Governments cannot openly avow this, because that would amount to admitting that herd immunity is the objective. And it is not yet even known whether and for how long infection confers immunity. Much better, then, to pursue this goal silently, under a cloud of obfuscation, and hope that a vaccine arrives before most of the population is infected.