History’s Biggest Natural Experiment

Faced with the threat of COVID-19, most coun­tries in the world are sud­denly, dra­mat­i­cally im­prov­ing their hy­giene and in­fec­tious dis­ease con­trol. This won’t just slow the spread of COVID-19. As a byproduct, it will also sup­press al­most ev­ery other con­ta­gious dis­ease. This cre­ates a nat­u­ral ex­per­i­ment, which an­swers the ques­tion:

What would hap­pen if we fully sup­pressed in­fluenza, the com­mon cold, and all the other ig­nored, minor in­fec­tious dis­eases, all at once?

About 13% of can­cers wor­ld­wide are at­tributable to known in­fec­tious causes. Many other health prob­lems are sus­pected to be re­lated to in­fec­tious dis­ease, in­clud­ing chronic fa­tigue syn­drome, type 1 di­a­betes, hy­pothy­roidism, obe­sity, Alzheimers dis­ease, bipo­lar di­s­or­der, and some mechanisms of ag­ing. (And obe­sity again but this time it’s a bac­terium in­stead of a virus.)

In the com­ing year, we’re go­ing to see large re­duc­tions in many dis­eases we never re­al­ized were in­fec­tious-dis­ease re­lated. As bad as COVID-19 is, this will be a pretty sub­stan­tial silver lin­ing.

Most of the dis­eases won’t stay gone; so­cial dis­tanc­ing and city­wide lock­downs are costly, and most dis­eases will re­tain enough reser­voirs to bounce back af­ter we re­turn to nor­mal. What we’ll get is a pe­riod we can study ret­ro­spec­tively, differ­ent in differ­ent coun­tries, in which al­most no dis­ease trans­mis­sion oc­curred.

This will be con­founded by COVID-19 it­self, of course. Peo­ple who them­selves had COVID-19 will have a lot of health prob­lems, which stud­ies will need to ac­count for. The iso­la­tion of so­cial dis­tanc­ing, the anx­iety of watch­ing the dis­aster un­fold, and the poverty of job-less and eco­nomic de­cline will leave their mark. In coun­tries where COVID-19 took hold, dur­ing the height of the pan­demic, can­cers and au­toim­mune di­s­or­ders and other con­di­tions will have been left un­di­ag­nosed due to the short­age of hos­pi­tals. We won’t eas­ily be able to tell which dis­eases matched with which health con­di­tions. With clever method­ol­ogy and ac­cess to data in coun­tries which had differ­ent out­comes, all of these is­sues will be pos­si­ble to work around.

The world’s at­ten­tion is now very fo­cused on the short term. Let’s give a lit­tle thought to what next year will look like.