The U.S. Centers for Disease Control and Prevention changed its mask guidelines Tuesday for people who have been fully vaccinated against COVID-19, citing new information about the ability of the delta variant to spread by those who have been vaccinated.
The CDC is now recommending that vaccinated people wear masks indoors again in parts of the U.S. where the coronavirus is surging and that everyone in K-12 schools wear masks, regardless of vaccination status.
CDC Director Dr. Rochelle Walensky said the high transmissibility of the delta variant is behind the agency’s change in guidelines.
"Unlike the alpha variant that we had back in May, where we didn’t believe that if you were vaccinated you could transmit further - this is different now with the delta variant. And we’re seeing that now, infection is possible if you (have been vaccinated and) are a rare breakthrough infection, that you can transmit further, which is the reason for the change," she said.
When earlier strains of the virus predominated, infected vaccinated people were found to have low levels of virus and were deemed unlikely to spread the virus much, CDC Director Dr. Rochelle Walensky said.
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, she continued.
Back in May, the CDC said that fully vaccinated people can stop wearing masks indoors in most settings and for months, cases, deaths and hospitalizations were falling steadily. But now the country is averaging more than 57,000 cases a day and 24,000 COVID-19 hospitalizations.
"We’re going in the wrong direction," Dr. Anthony Fauci, the nation’s top infectious diseases expert, said over the weekend.
Walensky reiterated several times Tuesday that the "vast majority" of transmission happening in the country right now is occurring through and among unvaccinated individuals.
Additionally, people who weren't vaccinated make up nearly all hospitalizations and deaths from COVID-19.
A small number of breakthrough cases are expected and health officials say they're not a cause for alarm.
In studies, the two-dose COVID-19 vaccines by Pfizer and Moderna were around 95% effective at preventing illness, while the one-shot Johnson & Johnson shot was 72% effective, though direct comparisons are difficult.
Most people with breakthrough infections experience mild illness, said Dr. William Moss, a vaccine expert at the Johns Hopkins Bloomberg School of Public Health.
The new guidelines Tuesday come as a growing number of cities and towns have restored their own indoor masking rules.
Earlier this month, Los Angeles County re-implemented its indoor mask mandate, regardless of vaccination status. St. Louis, Savannah, Georgia, and Provincetown, Massachusetts, are among the places that followed suit.
And as of this week, some government entities and companies have gone a step further to begin imposing vaccine mandates.
California and New York City announced Monday that they would require all government employees to get the coronavirus vaccine or face weekly COVID-19 testing, and the Department of Veterans Affairs became the first major federal agency to require health care workers to receive the shot.
It was unclear what would happen to employees who refuse to comply.
More than 163 million people, or 49% of the total U.S. population, are fully vaccinated, according to CDC data. Of those eligible for the vaccine, aged 12 and over, the figure rises to 57%.
Meanwhile, in a possible sign that increasingly dire health warnings are getting through to more Americans, vaccination rates began to creep up again this week, offering hope that the nation could yet break free of the coronavirus if people who have been reluctant to receive the shot are finally inoculated.
The Associated Press contributed to this report.