The Centers for Disease Control reversed course Monday and said it now recommends indoor masks for the vaccinated in all areas of the country where COVID infections are surging. CDC director Dr. Rochelle Walensky cited unpublished data from recent days suggesting that vaccinated people may be able to spread the Delta variant just as easily as unvaccinated people.

We're back in a phase of constantly shifting information and data — and just last week we had experts casting doubt on whether vaccinated and mildly symptomatic or asymptomatic cases should be counted as "breakthrough" cases, and others casting doubt on whether vaccinated people could spread the virus easily.

But as was expected, the CDC changed its tune about masking on Tuesday, recommending that vaccinated people resume wearing masks in crowded indoor settings. And, it should be noted, that while outdoor gatherings are still being considered safe, some experts are also now casting doubt on what assumptions to keep with the Delta variant. Dr. Eric Feigl-Ding, one of the world's leading epidemiologists, pointed to some recent "fleeting" transmission cases in Australia, albeit indoors, that appeared to happen with barely any close contact whatsoever.** And an outbreak of around 1,000 attendees at an outdoor music festival in the Netherlands appears to confirm that widespread outdoor transmission of the Delta variant is possible in crowds.

As the Associated Press notes, Walensky cited data from the last few days, still unpublished, taken from 100 samples from vaccinated and unvaccinated individuals with COVID infections. They found that the amount of virus in the noses and throats of vaccinated infected people was nearly "indistinguishable" from what was found in unvaccinated people, confirming what some experts have suspected. The increased viral load associated with the Delta variant appears to make vaccinated people equal spreaders of the virus. Walensky said that the data was "concerning enough that we feel like we have to act."

Infections in vaccinated people are still vastly less severe than those among the unvaccinated, and the overwhelming number of hospitalizations and deaths are happening among the unvaccinated. But new evidence is enough to make the vaccinated feel less secure about what happens if they're exposed to the Delta variant.

Last week, UCSF infectious disease expert Dr. Monica Gandhi tried to quell fears about infections in the vaccinated population, saying that some of these mild and asymptomatic cases could be turning up "dead viral particles in your nose" that trigger positive tests. And she questioned whether those cases are as worrisome or as noteworthy, public-health-wise, as those in unvaccinated people.

Gandhi also previously cautioned that the renewed hysteria among epidemiologists was reminiscent of the AIDS pandemic, and it took time to come up with mitigation measures that were less driven by panic. "The way that scientists are talking now was how scientists were talking at the beginning of the HIV epidemic," Gandhi said speaking to Slate. "It took some time, and everyone was scared and screaming, just like we are now, at the beginning of the HIV epidemic." *

Gandhi contributed to this piece today in the Washington Post, trying to parse the yo-yo guidance. "To get through this next stage of the pandemic as safely as possible, we’ll need to know when we can lift restrictions without sparking new surges. Fortunately, if we pay attention to some key metrics, we can figure that out," the authors write. They add that new mask guidance is about returning to an "acceptable" level of hospitalization and death, similar to the seasonal flu. "All pandemics end," Gandhi and her colleagues say. "The question is, how do we know when they do? These metrics will help us know when to begin to lift restrictions and get on track to a new normal."

So, again, we're in a place of wondering who to believe.

Speaking at a White House press conference today, Press Secretary Jen Psaki said that CDC continues doing what it is is supposed to do as data and the need for new guidance changes. "That is their job," she said. "Their job is to look at evolving information, evolving data, an evolving historic pandemic and provide guidance to the American public." She reiterated that being vaccinated remains the best protection against the virus.

As for whether San Francisco is considered a high-transmission area by the CDC right now, it is. According to the CDC's tracker, Alameda, Contra Costa, San Francisco and Solano counties are all areas of high transmission, while the rest of the Bay Area is in the "substantial transmission" category.

One more worry: For the last two days on Twitter, Dr. Feigl-Ding has been stressing studies out of England that suggest that COVID-19 infections appear to cause cognitive declines even among those who have mild or even asymptomatic cases — though the cognitive declines were sharper among those who were hospitalized with severe cases.

"Folks — gonna level with you — I would not want this for myself or anyone I know," Feigl-Ding said. "Death is not the only bad outcome of #COVID19 — even if we survive, there are huge chronic consequences... Avoid infection not just hospitalization!"

Furthermore, in today's new CDC guidance, they are now recommending masks for all teachers, staff, students, and visitors to schools, regardless of vaccination status.

Previously: Experts: Delta Not Likely Causing More 'Breakthrough' COVID Cases, and Maybe Asymptomatic Cases Shouldn't Count

Photo: Darwin Bell

*This article has been updated with additional context from Dr. Monica Gandhi.

**This article has been corrected to show that the fleeting transmissions thought to be documented in Australia were all indoors.