Thread by @NateSilver538

The news is *not* that "vaccinated people easily spread the Delta variant". That reflects a gross misunderstanding of the CDC's evidence, abetted by imprecise and innumerate media coverage. See this thread below.

https://twitter.com/JamesSurowiecki/status/1420991377702334464?s=19

https://twitter.com/Mikel_Jollett/status/1421144122807578627

Vaccinated people are much less likely to become infected with COVID. *Conditional upon becoming infected*, there is some evidence to suggest they carry similar viral loads, but this evidence is quite uncertain, and viral loads do not necessarily equate 1:1 to transmission.

Of course it doesn't help when The New York Times takes some new (not yet public or peer-reviewed FWIW) study that says what I wrote above and frames it as some "harrowing new twist that upends everything we know about the coronavirus" or whatever.

Here, finally, is the Provincetown study, which includes several major caveats, most of which are almost completely missing from the hyperbolic news coverage around this.

cdc.gov/mmwr/volumes/7…

There is also one major caveat that the study authors don't mention: they are only looking at *people who chose to be tested*, which is a lot different than *all breakthrough infections*. Presumably people with symptoms are much more likely to be tested.

*Symptomatic* breakthrough infections having similar viral loads to *symptomatic* unvaccinated infections would be much less of a problem, both because symptomatic breakthroughs are rare and because people can learn to be more careful (and get tested) when they have symptoms.

Finally I'd note that the sample sizes here are tiny, leading to very wide confidence intervals. And the "real life" confidence intervals are likely even wider given that (as the study authors say) the sample isn't very diverse. (P-town = mostly affluent middle-aged gay men.)

To take a self-selected, not-statistically-significant sample of ~200 nondiverse people during a party weekend that was an outlier in many respects, and use it to conclude that breakthrough infections are just as likely to transmit the virus, seems like quite the stretch.