Thread by @AstorAaron

Great thread rounding up newer studies on vaccine effectiveness v. infection and transmission since Delta arrived. Did VE drop bc of Delta? Or bc of waning effectiveness? Or both? And by how much? Read the whole thread!

https://twitter.com/AaronRichterman/status/1460456816211542025

One point mentioned in this thread that is lost in much discussion: For vaccinated people, the relative effectiveness (for infection) v. Delta is only slightly diminished compared to Alpha. But the absolute risk is much higher. You can see that in the many breakthrough charts.

Look at the blue line above. It stays far below the black line. Relative VE is still very strong! But note that blue line jumps from 8.47 weekly cases per 100k in June (pre-Delta) to 121.4 per 100k in late August (peak Delta wave). That's a 13X jump in ABSOLUTE risk for vaxxed.

All the "OMG breakthrough cases everywhere!" talk is bc of that jump in ABSOLUTE risk among the vaccinated. Chances are 13X higher you know somebody who got a breakthrough (or got one yourself) w/ Delta than before. BUT, that is NOT the same as "the vax doesn't work v. Delta."

This is where the dry tinder v. wet logs analogy is useful. When there is huge community transmission among non-immune people (dry tinder), the vaccinated among them (wet logs) are more likely to catch fire too. But at a much lower rate than the non-immune.

Complications for this data: What about previously infected but not vaccinated? Most studies show robust and long lasting infection-induced immunity. Consequence for VE: Presence of convalescents in non-vax pool mean real VE is even higher v. non-immune.

Very hard to separate out previously infected v. never-infected in the unvaxxed pool. Major differences by region too - consult covidestim.org for estimated levels of previous infection per county. Of course, this includes breakthrough infections + unvaxxed infections.

So when considering "absolute" risk in a community, need to look at both previous infection + vax, in addition to mechanics of epidemiological waves (~2 months, seasonal, community behavior, etc.).

What does this mean re: boosters? They dramatically increase antibody titers & reduce all infections to near zero - much like back in pre-Delta late Spring. For how long? Unknown. Re: severity waning is less, but still an issue for elderly. (Israel showed)

https://twitter.com/sailorrooscout/status/1460246290546270211?s=20

All of which is why I think it is right that boosters be made available for all 18+ but mandated for none. Leave it up to personal/family risk tolerance to decide. If non-elderly want/need avoid *any* infection (sympt or not)? Get a booster. Otherwise (non-elderly), not needed.