Engineers have a poor sense of the level of slop in biology and medicine. I can tell you with near 100% confidence how PCR works, but if I set out to run PCR in the real world (which is actually one of the most repeatable things in biology, btw), it's just going to fail some of the time, even if I've done the same exact reaction many times before. The biological world is noisy.
Remember the old physics joke about "assume a frictionless spherical horse"? This is a "spherical horse" of the pandemic. It's one of those things that armchair biologists take way too literally, because it's in a textbook. Obviously, first-year mechanics isn't wrong...it's just not all there is.
Working age population (205M): https://fred.stlouisfed.org/series/LFWA64TTUSM647S
Total population (328M): https://fred.stlouisfed.org/series/POPTOTUSA647NWDB
Under 15 (~60M): https://datacenter.kidscount.org/data/tables/101-child-popul...
* 33% of the US population has had at least one dose (19% are fully vaccinated).
* 42% (25%) of the population over 18.
* 76% (57%) of the population over 65 (who are, not incidentally, by far the most likely to experience mortality):
https://covid.cdc.gov/covid-data-tracker/#vaccinations
These numbers are rapidly increasing, and on top of the ~100-120M that have been infected in the US already (current CDC estimates are that actual cases are around 4x the number reported [1]). And of course, as I said, it's not as if "herd immunity" is a single number that is the same everywhere in the US.
Nobody claimed that we're there yet, but given all current data, pessimism is unwarranted.
[1] https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/geog...
> > So can we have "herd" immunity when the majority of the able-bodied working-age population and school kids are not protected yet?
> Yes.
Yes. It's been one of the dumbest narratives of the last year that "herd immunity" is a single, fixed constant determined solely by vaccination rate. It isn't. The threshold itself is going to differ by subpopulation, and is affected by population mixing, mobility, climate, age distribution, current disease prevalence, natural infection rate and lots of other factors. For example, it's quite possible that large pockets of rural areas will achieve "herd immunity" long before, say, London, simply because there are fewer people interacting on a daily basis.
Even then, it's not like you hit the threshold, and infections just drop off dramatically. It's a shift as you get closer to the "threshold" (whatever that actually is), with infections gradually falling toward (but likely never reaching) zero.
This toy model version of herd immunity is appealing to the Thomas Pueyos of the world, but not at all representative of what happens in messy reality.