CDC: Mask up, even if vaccinated
Guidance on indoor use changes in light of new data on transmission
The Centers for Disease Control and Prevention on Tuesday reversed its earlier guidance and recommended that everyone, regardless of vaccination status, wear masks indoors in regions where the coronavirus is spreading fast, based on evidence that people who are fully vaccinated can be infected with the delta variant and pass it to others.
The federal policy shift shouldn’t have much immediate impact in the Bay Area, where vaccinated residents in eight of nine counties already have been advised to resume wearing masks in indoor public spaces. And California earlier this month said it would require all K12 students, teachers and staff to wear masks in school this fall — a move that at the time went beyond CDC recommendations.
The updated CDC guidance takes into account increasing signs that the delta variant,
believed to be up to twice as infectious as the original coronavirus strain, is better able to infect people who are fully vaccinated, and that those people may be just as able to transmit the virus to others as those who aren’t vaccinated.
Even against delta, the vaccines remain highly effective at preventing serious illness resulting in hospitalization and death, health officials said. But people who are fully vaccinated should wear masks in all indoor public spaces where the virus is widespread — including the Bay Area and most of the rest of California — to prevent becoming infected and to reduce the chance of infecting others.
“The delta variant is showing every day its willingness to outsmart us,” said Dr. Rochelle Walensky, director of the CDC, in a news briefing Tuesday. “In recent days, I have seen new scientific data showing ... that the delta variant behaves uniquely from past strains.”
The CDC did not release data on postvaccination breakthrough infections and transmission on Tuesday. But Walensky said investigations of large outbreaks in the U.S. have found that some people who test positive despite being vaccinated have as high a viral load as those who were not vaccinated. That wasn’t the case with earlier variants, including the highly infectious alpha that was previously dominant in the U.S. The delta variant now makes up about t0% of cases in the United States.
“We believe the vast majority of transmission is in and through unvaccinated people,” Walensky said. “But unlike the alpha variant, where we didn’t believe if you were vaccinated you could transmit further, this is different now with the delta variant.”
When investigators looked at the viral load in those who were and were not vaccinated, “We’re seeing they’re quite similar,” Walensky said. “That leads us to believe that the breakthrough infections, rare as they are, have potential to forward transmit with the same capacity as an unvaccinated person.”
The CDC guidance is meant specifically for parts of the country where transmission is widespread — in the red “high” or orange “substantial” categories of the federal system for tracking cases and other metrics of the pandemic. Most of California, including all of the Bay Area, falls into the red or orange categories.
Health officers in eight Bay Area counties already had advised residents earlier this month to start wearing masks again indoors, even if they were fully vaccinated× Solano County has not yet issued such guidance. The Bay Area mask guidance is not yet a mandate. In California, only Los Angeles County is requiring masks indoors for everyone.
California also announced it would require masks in K12 schools, though the CDC before Tuesday’s reversal had not recommended them in schools for people who are vaccinated.
The mask recommendations in California were largely in response to growing concern over a fourth surge of the pandemic, fueled by the alarmingly infectious delta. Cases have increased more than fivefold in the Bay Area and statewide since California dropped almost all public health restrictions on June 15. COVID hospitalizations have more than tripled.
In addition to reviving mask advisories, health officials are urgently trying to increase vaccinations. On Monday, Gov. Gavin Newsom said all state employees would be required to show proof of vaccination or undergo at least weekly testing starting next month. And on Tuesday, the California State University system said it would require all students, staff and faculty to be vaccinated this fall.
The CDC’s mask advisory wasn’t surprising to health experts, many of whom said the guidance should have been revised weeks ago. But several experts said Tuesday that evidence of delta spreading from vaccinated people was gamechanging. In particular, it means vaccinated people need to take care that they don’t pass the virus to people who aren’t inoculated, including children under age 12 who aren’t eligible for the shots.
“You can think of the vaccine and the mask together as bringing the viral load down,” said Nadia Roan, a UCSF immunologist and investigator at the Gladstone Institutes in San Francisco. “They will protect you from transmitting to others more so than if you had one, or neither.”
Roan and other experts also noted that masks are a relatively simple tool for reducing transmission, especially as more data emerges about delta and how it spreads. Better to renew mask urgings than employ more aggressive measures like banning large gatherings or issuing capacity limitations that could harm businesses, experts said.
“The public needs to realize as the virus evolves and mutates, the public health response needs to adapt,” said Dr. Abraar Karan, a Stanford infectious disease expert. “Vaccines reduce the probability that you transmit the virus, but they don’t bring it to zero. Masks are relatively low hanging fruit that can be implemented and turned on and off as cases can go up and down.
“People need to get used to this as we head back into the winter,” he added. “We may see again that we have higher rates of transmission.”