Nearly 600 patients wait for hospital beds in Houston following surge in COVID cases

Hours after the Centers for Disease Control and Prevention officially recommended a third dose of an mRNA vaccine for immunocompromised Americans, both Walgreens and CVS said Friday they will be able to administer third doses of the Pfizer and Moderna vaccines to eligible patients.

Walgreens said walk-ins are welcome now at select locations, while CVS said appointments will be available starting Saturday.

Both companies said patients should be prepared to prove their eligibility for a third dose.

-ABC News' Sasha Pezenik

Oregon Gov. Kate Brown said Friday she is deploying up to 1,500 members of the National Guard to help hospitals throughout the state "overstretched by patients during the delta surge."

"I cannot emphasize enough the seriousness of this crisis for all Oregonians, especially those who might need emergency or intensive care," Brown said in a video message. "When our hospitals are filled with COVID-19 patients, there may not be a room for someone needing care after a car crash or a heart attack or other emergency situation."

As of Friday morning, there were 733 people hospitalized with "severe cases" of COVID-19, including 185 patients in the intensive care unit, Brown said.

The Oregon Health Authority and the Oregon Department of Human Services are also working to provide support to hospitals, and Brown said she is requesting FEMA support.

In the meantime, the governor urged people to wear a mask while in public and get vaccinated if they haven't yet.

The American College of Physicians said Friday that masks should be required in all schools "as part of a comprehensive effort to reduce the spread of COVID-19."

The statement follows similar recommendations from the American Association of Pediatrics and the Centers for Disease Control and Prevention, and comes as some school districts have been defying bans on masks mandates in states including Texas and Florida.

"Masks are a key public health tool in keeping everyone in our school communities safe," ACP President Dr. George Abraham said in a statement. “Especially with such a large segment of our schools’ populations unable to yet access COVID-19 vaccines, masks remain a necessity in our fight to control the COVID-19 pandemic."

The ACP is the largest medical specialty society in the U.S., with over 161,000 internal medicine members.

The Centers for Disease Control and Prevention's advisory panel voted unanimously Friday to recommend an additional dose of Pfizer or Moderna for immunocompromised people. (This recommendation applies only to people who already had an initial series of mRNA -- it does not apply to people who received J&J.)

Immunocompromised people will not need a doctor's note, prescription or proof of their condition to get their third dose, CDC officials said at Friday's meeting.

"This is a self-attesting. We do not anticipate -- we are not recommending that either prescriptions or a physician sign off, or be necessary for individuals to receive an additional dose of mRNA if they're immunocompromised," said Dr. Kathleen Dooling, Medical Officer for the Division of Viral Diseases, the National Center for Immunization and Respiratory Diseases, and the CDC.

CDC Director Rochelle Walensky signed off on the recommendation later on Friday.

-ABC News' Cheyenne Haslett, Sasha Pezenik