This is the crux of the new guidance. A few weeks ago, after L.A. County reimposed an indoor mask mandate, I wrote, “The million-dollar question is whether vaccinated people who are infected but experiencing few or no symptoms are capable of passing the new variant to others. A study of Delta published this week showed that infected unvaccinated people shed a thousand times as much virus with the Delta strain as they did with the original SARS-CoV-2. How much are vaccinated people shedding by comparison?”

Today we have an answer. They’re shedding enough to infect people around them on “rare occasions,” CDC chief Rochelle Walensky told the media. Which is … not very precise when defending a new national policy.

How rare are these “rare occasions”? Evidently they’re common enough that they require asking potentially every vaccinated person in the U.S. to mask up again.

BREAKING: CDC Dir. Walensky says new information "indicates that in rare occasions some vaccinated people infected with the delta variant after vaccination may be contagious…This new science is worrisome and unfortunately warrants an update to our recommendations." pic.twitter.com/NoytopXni4

— ABC News (@ABC) July 27, 2021

There’s a new million-dollar question. (Besides “How rarely are the vaccinated infecting others?”) Are the vaxxed infecting only the unvaccinated or are they also infecting other vaccinated people? Logically we’d expect an infected unvaccinated person to shed lots more virus than an infected vaccinated one since the unvaxxed don’t have antibodies attacking the virus immediately to reduce its strength once it enters the body. Still, per Walensky, sometimes even the smaller amount of virus shed by a vaccinated person is enough to infect someone else. No doubt another vaccinated person is considerably harder to infect with that smaller viral load due to the antibodies they have than an unvaccinated person is.

If the vaccinated are capable of infecting only the unvaccinated then there’s a strong argument that the new mask guidance is unfair. With few exceptions, everyone who’s still not immune from COVID at this point is that way by choice. Younger kids aren’t immune since they’re ineligible for the vaccine at the moment but younger kids almost never have a problem with the virus. Which means the new mask guidance is essentially asking the vaccinated to protect unvaccinated adults from the consequences of their own folly and obstinacy.

Why should they? If you haven’t gotten your shots, you’ve knowingly assumed the risk of being infected. I shouldn’t have to wear a mask to reduce the jeopardy in which you’ve willingly placed yourself.

But if the vaccinated are capable of infecting other vaccinated people because Delta is so super-contagious, the calculus changes. If you know you can give the virus to your vaccinated grandma, maybe you want to hedge against that risk even though it’s unlikely that she’d come down with a serious case from it. Older people’s immune systems are less resilient so she may be laid up for awhile, and even “mild” cases of COVID can be unpleasant in ways that the flu isn’t. Some people afflicted by the disease find that everything smells like garbage for months (or years?) afterward. Is it worth wearing a mask to reduce the chance of that happening to grandma — or to you?

The CDC thinks it is, although they’re kidding themselves about how this guidance will shake out on the ground:

CDC recommends vax’d folks wear masks indoors in places with “substantial” and “high” transmission.

“Substantial”: 50-100 cases per 100,000 people over seven days

“High”: More than 100 cases

If your county is orange or red on this map, it would qualify. https://t.co/nYNQ0Zacms pic.twitter.com/Co1ipTUbhJ

— Dan Diamond (@ddiamond) July 27, 2021

As with everything, the risk-averse will mask up in response to Delta regardless of the official guidance while the risk-tolerant will continue to go barefaced. To the extent today’s new recommendations matter at all, it’ll simply be as a signal that the feds are now officially Concerned about the spread of the variant. Which, maybe/hopefully, will encourage people to go out and get vaccinated. The hot take among righties this afternoon is that the CDC endorsing masking for vaccinated people will disincentivize vaccination but I’m not so sure. It may be received by holdouts as more of a “the sh*t is about to hit the fan” message, leading them to go out and get their shots ASAP. Remember, after a long period of decline, daily vaccine doses in the U.S. finally leveled off this week. Jitters about Delta have moved some people into the vaccination camp.

Biden also stressed today in a statement that vaccination, not masking, is the only real solution:

Statement by President Joe Biden on CDC Guidance pic.twitter.com/GBUD3hObxS

— CSPAN (@cspan) July 27, 2021

Republican pols have already countered by insisting that they won’t condone masking the vaccinated, especially in the form of state mandates:

Don’t expect any mask mandates in Iowa. Governor Kim Reynolds says CDC’s new guidance is “not grounded in reality or common sense.” pic.twitter.com/rpUPdF2xCO

— Tony Leys (@tonyleys) July 27, 2021

Ted Cruz on the CDC's new mask guidance: "The CDC has lost its credibility when it comes to what decisions Americans should make about COVID-19. It’s long past time we got back to trusting the American people…" pic.twitter.com/z8EVOYbEKV

— Andrew Solender (@AndrewSolender) July 27, 2021

If over 99% of Covid deaths are among the unvaccinated how does forcing the vaccinated to wear a mask make any sense?

And if you thought it was hard to convince people to get vaccinated before, imagine now that being vaccinated still means wearing a maskpic.twitter.com/SoYB6cS8QL

— Marco Rubio (@marcorubio) July 27, 2021

Psaki does a terrible job of stating the case in the clip tweeted by Rubio. Is the White House arguing that the vaccinated should mask up to protect the unvaccinated? Or are they arguing that the vaccinated themselves are at meaningful risk of an unhappy bout of COVID if they don’t mask? Who, primarily, are the feds trying to protect with the new policy? Because the answer’s going to be uncomfortable morally or scientifically depending upon which it is.

The Times has a little more on the changing science that prompted today’s guidance:

C.D.C. officials were swayed by new research showing that even vaccinated people may carry great amounts of the variant virus in the nose and throat, hinting that they also may spread it to others.

Large so-called viral loads may help explain reports of breakthrough infections in groups of vaccinated people. For example, an outbreak that began in Provincetown, Mass., after Fourth of July festivities there has grown to include at least 765 cases, according to Steve Katsurinis, chair of the Provincetown Board of Health…

[Walensky] acknowledged that some vaccinated people can become infected with the Delta variant and may be contagious, but maintained that it was a rare event. But the C.D.C. is tracking only breakthrough infections that lead to hospitalization or death among vaccinated Americans. Officials have previously said that vaccinated people account for just 3 percent of hospitalizations.

How bad are the symptoms typically in breakthrough cases that fall short of requiring hospital care? The CDC doesn’t know because they’re not tracking them. If you’ve been vaxxed and get infected with Delta, are you facing a week of flu or a month of being winded when you climb stairs or three months of not being able to smell anything or some sort of long-term cognitive impairment? Whether you should bother masking depends on the probable severity of symptoms in “mild” cases. In all likelihood, in most cases the symptoms won’t be very bad at all.

With the current variant, I mean. Walensky’s already looking ahead to the nightmare scenario:

With unmitigated spread, Walensky warns that COVID could be “just a few mutations away” from potentially being able to evade vaccines entirely.

— Scott Bixby (@scottbix) July 27, 2021

I saw something the other day that suggested Pfizer and Moderna could have new mRNA vaccines capable of defeating a killer variant within 100 days of its detection, which is phenomenal. But those 100 days will feel a lot like 2020.

Here’s a little more from Walensky’s phone call today, in which she mercifully reiterated that school should be in-class full-time this fall. They’re not backing away from that guidance — yet. Exit question via Ross Douthat: Since COVID is destined to be endemic, does this mean we’ll be asked to mask permanently to protect the unvaccinated? Or are we still expecting to reach herd immunity through natural infection and end up with chronically low cases across the population?

Dr. Rochelle Walensky: “CDC recommends that everyone in K-12 schools wear a mask indoors, including teachers, staff, students, and visitors, regardless of vaccination status.” pic.twitter.com/IXOIEGVGj0

— The Post Millennial (@TPostMillennial) July 27, 2021