This explanation from the CDC is remarkable:
CDC's Dr. Walensky says guidance for fully vaccinated people to wear masks indoors/mass gatherings is largely to protect unvaccinated from other unvaccinated folks who may be there (given difficulty distinguishing vaccinated people from those that aren't)
— Zeke Miller (@ZekeJMiller) April 27, 2021
This isn’t “science.” It’s practical politics, the sole purpose of which is to try to guess how people will behave in the real world and drive them toward a preferred outcome. If it were based upon the science, it would hold that people who have been vaccinated do not need to wear masks and that those who have not been vaccinated do. That, and not lumping them in all together, is the policy that the evidence demands.
Why does this matter? Well, because after a while people notice. When you tell people not to buy masks because you want to ensure that there is a sufficient supply for the medical profession, you make it much more difficult to tell everyone that masks are imperative when the practical considerations change. So it is here. I can see why the CDC thinks a one-size-fits-all approach will be effective. But at what cost?
The vaccine works incredibly well, and yet, because it is obsessed with trying to work out how people think, the CDC is failing to properly convey just how effective it is in protecting people from contracting or transmitting the virus. I am sure that, at the margins, there are some downsides to a more simple (and more accurate) message, such as “get the vaccine, get back to normal.” But surely they cannot be higher than those imposed by the current confusion. To tune in to any public-health briefing is to be told that the vaccine works, and that it’s important that you choose to get it, but that if you do you won’t be able to do anything you did before. When, eventually, the CDC switches to a flat-out “vaccines work” message, a lot of people aren’t going to believe it.