Some people still need to mask up even if vaccinated. Are you one of them?

The news flashed across the country – mask-free at last!

People who are fully vaccinated against Covid-19no longer have to wear masks inside or outside, nor do they have to stay 6 feet away from others, according to new guidance released Thursday by the US Centers for Disease Control and Prevention.

Shoppers wearing protective masks push shopping carts inside a Costco store in San Francisco, California, U.S., on Wednesday, March 3, 2021. Costco Wholesale Corp. is schedule to release earnings figures on March 4.

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Does that mean those Americans vaccinated at least two weeks ago – meaning full immunity has kicked in – can throw their masks in the air and hug all in celebration?

Not quite.

You do have to mask up on public transportation or if required by laws or regulations – that would apply to hospitals, nursing homes and other health care settings, and even some local businesses and workplaces. Kids still have to mask up to go to school.

Then there is this warning: “If you have a condition or are taking medications that weaken your immune system, you may NOT be fully protected even if you are fully vaccinated. Talk to your healthcare provider,” the CDC said in the new guidance. “Even after vaccination, you may need to continue taking all precautions.”

On CNN’s State of the Union Sunday, CDC Director Dr. Rochelle Walensky said that immunocompromised people should consult with their physicians before deciding to stop wearing a mask, but others, including those at higher risk for severe Covid-19, may want to do so, as well.

For the most part, studies emerging now suggest immunocompromised people or those on medications that interrupt their immune system – for example, people who have had organ transplants or are on chemotherapy – may not have as much protection from Covid-19 vaccines. At least one study suggests dialysis patients also may not be as protected, she said.

Immunocompromised

Some people may still need to wear masks.

There are a number of conditions that can weaken immunity.

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Some diseases, like HIV/AIDS, can completely devastate the body’s ability to fight infection. Organ transplant patients must take daily medications that suppress the immune system to keep it from rejecting the new organ. And chemotherapy works by killing cell growth to keep cancerous cells from multiplying, thus weakening the immune system.

“In addition to chemotherapy, certain types of immunotherapy, stem cell or bone marrow transplants, and other medicines can severely weaken the immune system,” said Laura Makaroff, the senior vice president for prevention and early detection at the American Cancer Society.

People who are severely immunocompromised are told they must remain fully masked and take extra precautions to be protected from all manner of pathogens, and they wish the rest of us would mask up to protect them, too.

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Common conditions that weaken immunity

Many common diseases and conditions that affect millions of Americans can weaken the immune system, typically to lesser degrees. The body may respond listlessly to invaders, making it more vulnerable to infection and viruses such as Covid-19.

KENNEBUNK, ME - JANUARY 9: Staff and residents at Atria Senior Living in Kennebunk receive their first doses of Pfizer's COVID-19 vaccine during a clinic administered by CVS professionals on Saturday, Jan. 9, 2021. A nurse displays at sticker after receiving the vaccine shot. (Staff photo by Derek Davis/Portland Press Herald via Getty Images)

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Diabetes, for example, can lower immunity: There are 34.2 million people living with diabetes in the US; another 88 million have prediabetes, according to the CDC.

Not all of them have frail immune systems, but some do. One of them is Alyannah Buhman, who told CNN last August that worry over Covid-19 left her “very on edge.”

“I get sick really easily,” she said. “I cannot fight off anything to save my life. I start puking everywhere. It’s a terrifying thought.”

Obesity can be tied to feeble immunity as well – over 40% of Americans are obese – as can chronic kidney disease, liver and heart disease, and old age.

When it comes to cancer, both current patients and survivors should check with their doctor before removing masks and other protection, Makaroff said.

“For people who have a weakened immune system, either from cancer itself or treatment, you may be not fully protected even if you are fully vaccinated. It is important to talk with your health care provider about which precautions you still need to take,” she said.

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Heart disease is the number one killer of men and women in the US, but unlike cancer, “the medications used to treat heart disease, for the most part, are not immunosuppressive, and should not pose any particular risks,” said American Heart Association President Dr. Mitchell Elkind.

“Patients with heart disease are at increased risk of adverse outcomes from Covid-19, but they have the same benefits from vaccines as those without heart disease,” Elkind said.

“We recommend that patients with heart disease who have been vaccinated, and are not immunocompromised for some other reason, follow CDC guidelines regarding wearing masks and social distancing,” he said.

Because pregnant women are at higher risk for severe Covid-19, Walensky said that the CDC is encouraging them to get vaccinated, and the decision to go unmasked would be an individual one.

Autoimmune medications

Millions of Americans live with common autoimmune conditions such as “psoriasis, rheumatoid arthritis, scleroderma, inflammatory bowel disease, Crohn’s disease, ulcerative colitis and lupus,” said Dr. Cedric “Jamie” Rutland, a pulmonary and critical care physician.

CHICAGO, ILLINOIS - APRIL 26: People walk through Chicago O'Hare airport on April 26, 2021 in Chicago, Illinois. As the number of the people vaccinated against COVID-19 increases throughout the nation, people are beginning to travel by air again. Nearly 1.6 million Americans flew on April 18, 2021 while just over 105,000 Americans flew on the same day in 2020. (Photo by Spencer Platt/Getty Images)

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In autoimmune disorders, the immune system goes awry, mistakenly ordering its army of warriors to attack the person’s own body.

Medications often used to treat autoimmune disorders are built to suppress that overzealous immune response – but it’s not targeted. Instead, the drugs weaken the entire immune system, leaving the body vulnerable to upper respiratory and urinary tract infections, pneumonia, skin infections and, of course, Covid-19.

A few studies have also found that by dampening immune response, people who are on medications for autoimmune diseases may not “have as strong of a response to the Covid-19 vaccine,” said Rutland, the medical director of the Rutland Medical Group in Newport Beach, California.

A small study of 26 people with inflammatory diseases found levels of coronavirus antibodies were slightly lower in those patients compared to others, but no one was a “complete non-responder.”

A larger study of 133 people found a “three-fold reduction” in antibodies to Covid-19 compared to healthy controls, with some medications, such as glucocorticoids, worse than others. Still, the antibodies found in patients on medications were “comparable to patients with rapid recovery from COVID-19 and may, therefore, provide sufficient humoral protection,” the study said. The study was a pre-print, meaning it has not been vetted by a journal for publication.

While vaccination appears to be effective, Rutland said he plays it safe with his patients: “I take them off of those (autoimmune) medications before they get vaccinated, so they can have the appropriate immune response,” he said.

In the end, how do you decide if you fit into the category of “weakened immune system”? How can you know if you should think twice about joining the maskless masses?

“What we would recommend is certainly for people who have immune compromising diseases or on those medications to consult their physicians,” Walensky said.

“Really, again, not everybody has to rip off their mask because our guidance changed on Thursday,” she said. “So, yes, if you are concerned, please do consult your physician before you take off your mask.”

CNN’s Ryan Prior and Virginia Langmaid contributed to this report.