I missed this detail from Rochelle Walensky’s press conference earlier but it helps explain why the CDC is suddenly nervous about vaccinated people going around unmasked.

It’s getting attention online this afternoon too, partly because Drudge is highlighting the news and partly because excited vaccine skeptics are misunderstanding what it says, I suspect. When the CDC says that the vaxxed and unvaxxed have the same viral load, they don’t mean they have the same amount throughout their bodies, including their lungs. That would mean the vaccines don’t work, which is why anti-vaxxers have perked up about it. But we already know that they work: The numbers prove that the vaccinated are at far less risk of serious illness than the unvaccinated are. Delta usually can’t get enough traction in a vaccinated person’s body to debilitate them.

What the CDC means is that the vaxxed and unvaxxed have similar amounts of viral particles in their noses and throats, making them equal risks to infect the people around them. That’s a big deal and it helps explain the change in mask guidance. If the vaccinated are as likely to infect an unvaccinated person as another unvaccinated person is then reducing infections requires everyone to mask up, not just those who haven’t had their shots. The average vaccinated person would respond to that by saying, “Why should I care if I infect someone who’s unvaccinated? That’s their problem.” Fair enough, but epidemiologists are thinking big-picture. They want to slow the Delta surge as much as they can and buy time for vaccine holdouts to go get immunized before they’re infected.

But with the delta variant, the level of virus in infected vaccinated people is “indistinguishable” from the level of virus in the noses and throats of unvaccinated people, Walensky said.

The data emerged over the last couple of days from over 100 samples from several states and one other country. It is unpublished, and the CDC has not released it. But “it is concerning enough that we feel like we have to act,” Walensky said.

Vaccinated people “have the potential to spread that virus to others,” she said.

With previous strains of the virus, the vaccines were strong enough to reduce the viral load in immunized people to the point where they were basically no risk to transmit it to others. Not so with Delta. Some researchers believe that the high viral load in vaccinated people with Delta may include lots of dead viral particles, which might still show up in a test despite having already been neutralized by the immune response provoked by vaccination. The CDC evidently believes differently.

Drudge is touting a second bit of news today that has anti-vaxxers intrigued but this one’s less interesting than the viral-load comparison. It turns out that in California some highly vaccinated counties are seeing higher case rates than less vaccinated counties are. Proof that the vaccines don’t work?

A new analysis finds several counties with above-average vaccination rates also have higher COVID case rates, while case rates are falling in counties with below-average vaccination rates.

Statewide data analyzed by the Bay Area News Group found five counties, Los Angeles, San Diego, Alameda, Contra Costa, and San Francisco, have both a higher percentage of people who are fully vaccinated than the state average and a higher average daily case rate.

Compare that to these five counties: Modoc, Glenn, Lassen, Del Norte, and San Benito, which have below-average vaccination rates and decreasing case rates.

The five counties with low case rates are among the smallest in California, with around 60,000 people or fewer. The five with higher case rates are among the biggest, with 880,000 people or more. It’s probably a simple matter of mostly unvaccinated people getting infected much more quickly in denser areas due to Delta being hyper-contagious. Throw a house party in L.A. County and several hundred (young, probably mostly unvaxxed) people may show up; within a few hours they may all be infected. How many parties of that size are being thrown in Modoc County?

It reminds me of the anxiety people feel when there’s a report out of Israel of a surprisingly high percentage of vaccinated people in the hospital with COVID. The greater the share of the population that’s been immunized, the less surprising that should be for basic mathematical reasons:

Folks, if you’re vaccinated—and if I know critics, they were skipping all the lines they could to get vaccinated ASAP—you really have nothing to worry about, statistically speaking, even if you’re hearing about some vaxxed people getting COVID. Bayes Theorem is your friend. pic.twitter.com/ezn4UQ8PZF

— Sonny Bunch (@SonnyBunch) July 24, 2021

If the CDC is hellbent on trying to influence public behavior due to Delta, I think it would have done better to emphasize two points. One: Because older people have weaker immune systems, you might want to consider masking up around them even if they’re vaccinated. They’ll probably be okay if you infect them but they’re more of a crapshoot than the rest of the population. And two: If you’re going to mask, wear a real mask. A piece of fabric from CVS won’t do much to prevent infecting others with a variant that produces a thousand times as many viral particles as the original SARS-CoV-2 did. Wear an N95. They’re widely available — for the moment.

And, of course, get vaccinated to protect yourself:

In non-rare earth news: Louisiana pharma distributor contact tells me that vaccine orders have doubled in last two days and nearly tripled from last week.

Expect big jump in vaccination rate over next few days ..

— Brian Sullivan (@SullyCNBC) July 27, 2021

Exit question: Who’s more culpable for today’s new mask guidance, health bureaucrats or the unvaccinated?