# COVID-19 Group Testing Post-mortem?

As Covid is for the most part over and tests have not been in short supply for a very long time now, eliminating most of the rationale for complicated testing procedures meant to optimize test count/cost, it would be interesting for anyone who was involved in this to do a retrospective or post-mortem. Was pool testing useful? Why or why not? Can it be improved for future pandemics and should we care about it?

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My impression, not having paid much attention to the details at the time (AI scaling was more important), is that various group/pool testing approaches were useful in a few niches, but were rendered useless in many places due to politics/organization/social flaws, and didn't apply to most places.

1. I read that use of pool testing was common in China early on in 2020 as part of the hotspot strategy to economize on testing extremely large groups of people where only a few would have active Covid. This is the most logical place to apply it, and it was a major government & societal priority, so that is a success.

    I get the impression that they were able to switch to individual testing fairly early, in order to get faster turnaround and do more localized testing. But to the extent that pool testing was effective *from the start*, before testing manufacturing could scale up, and helped squash Covid when it was still squashable, then it was very valuable even if obsoleted.

    Of course, this evaluation can change depending on how Covid ultimately shakes out in China. Was it part of a heavyhanded but ultimately highly effective Covid Zero policy which led to it turning into a hermit country enduring devastating economic fallout while merely postponed the inevitable variant which could defeat Covid Zero? In which case, pool testing was a tool which played a part in buying China entire years to vaccinate but its good was rendered useless when they bizarrely failed to make any good use of the time, dabbling in ineffective vaccines etc, and in practice, only doubling down repeatedly on coercive testing and surveillance until the martingale blew up in their face. Or was it part of a visionary resolute effort which spared China the mass death of the rest of the world as it came out the other side by persisting so long in country-wide lockdown until Covid just sorta stopped being a problem somehow? Then its good was unalloyed and it's sad so few other countries could boast a better record (eg Taiwan; I dunno if they made any use of it).
2. Sewage/water testing in places like colleges: various universities or towns made heavy use of what is in effect pool testing to do mass screening of water to detect infections and then hotspot them. This was only useful as long as you have a baseline of ~0, otherwise testing water merely gives you a proxy for overall infections, which is a lot less useful than using it to detect & squash hotspots. In individual cases of orgs with great discipline, this apparently worked well, and avoided the need for constant individual testing (which was expensive, not possible early on, and still inadequate - as all the infections inside 'bubbles' show, just too much leakage, test error, incubation, idiosyncrasies and so on).

    Since most of these places were in countries where Covid became endemic eventually anyway, and everyone got infected, and in cases like colleges the young students were the last to get vaccinated (because they are the least harmed) and so needed to buy a lot of time to avoid infection before vaccination (which probably didn't happen for most of them), these success stories seem to boil down to just buying time, which is a good deal less impressive.

At the margin, doesn't seem like improvements to pool testing would have helped much compared to other things like faster vaccination approval.