Vaccinated Massachusetts residents with weakened immune systems, or who are otherwise at risk of complications from COVID-19, as well as unvaccinated students and staff should return to wearing facial coverings indoors, according to new state guidance released Friday.

"If you have a serious health condition or a serious risk of developing severe illness from COVID, you should take extra precautions," Gov. Charlie Baker said at a press conference in Roxbury Friday afternoon.

The Department of Public Health's new mask guidance comes days after the Centers for Disease Control issued similar recommendations warning that the Delta variant poses a threat even to vaccinated individuals.

The new guidance recommends that "a fully vaccinated person wear a mask or face covering when indoors (and not in your own home) if you have a weakened immune system, or if you are at increased risk for severe disease because of your age or an underlying medical condition, or if someone in your household has a weakened immune system, is at increased risk for severe disease, or is unvaccinated."

"As long as there are unvaccinated people in Massachusetts," Baker said, "we're likely going to see additional positive cases. But thankfully, a high vaccination rate here resulted in far fewer people getting sick."

The state is also increasing precautions for school children returning to classrooms in the fall. The Department of Elementary and Secondary Education issued a recommendation that students from kindergarten through sixth grade wear masks indoors. DESE is recommending that vaccinated students remain unmasked at schools, but vaccines are not yet available to children under the age of 12.

Baker said he fully expects cities and towns to make adjustments to conform to what's right for each individual school district.

"But one thing is clear, all schools and all districts must be open every day to every student, no matter what," Baker said.

Baker said the educational and social loss for students after more than a year of remote and hybrid learning should not be repeated.

Teachers unions immediately rejected Baker's new guidance for schools, with the Massachusetts Teachers Association calling Baker's recommendation "reckless" for only suggesting that unvaccinated teachers, students and staff wear masks.

"Rather than adopt a plan in line with the guidance issued by the Centers for Disease Control and Prevention and the American Academy of Pediatrics, DESE is essentially signaling that students, educators and families should not take seriously the reality of the alarming rise in the number of cases of COVID-19," wrote MTA president Merrie Najimy in a statement.

The Massachusetts chapter of the American Federation of Teachers wrote that DESE "needs to listen to health experts, including the CDC and the American Academy of Pediatrics, and require — not just recommend — universal mask wearing in K-6 schools this fall."

The AFT wrote that local schools "need to step up and require universal mask wearing to keep us all safe and to maximize the likelihood of schools staying open this school year."

The bottom line is that teachers' unions want Baker to adopt the broadest possible interpretation of CDC guidlines and strongly recommend that all persons in schools be masked at all times.

Baker said he has no intention at the moment of seeking another round of emergency powers that would enable him to issue mandates. His emergency executive authority ceased June 15.