Federal health officials this week cleared the way for patients to choose among all three vaccine options when boosting their COVID-19 immunizations.

The question now is: Which one?

Doctors say the answer depends on everything from individual health risks and concerns over rare side effects to vaccine availability. The bottom line, they add, is that having a choice is a good thing.

"The advantage of it is preference, ease of administration — just the technical feasibility of saying: Which vaccine would you like?" said Dr. Gregory Poland, a vaccine immunology specialist at Mayo Clinic.

The Centers for Disease Control and Prevention recommended Thursday that people who received the COVID-19 vaccine made by Moderna are eligible for boosters under the same guidelines as for those who initially received Pfizer vaccines. In both cases, boosters are recommended six months after the initial vaccine series for those 65 and older as well as adults age 18 to 64 who live in long-term care, have certain underlying medical conditions or face high risk of coronavirus exposure and transmission at home or work.

The Pfizer and Moderna vaccines, which are delivered in two doses initially, have been the most popular options in Minnesota, accounting for 60% and 36% respectively of all doses administered. For those vaccinated with the single-dose vaccine from Johnson & Johnson — about 290,000 people in Minnesota — the CDC said boosters are available to all those 18 and older who were vaccinated two or more months ago.

The CDC said it would allow mixing and matching with boosters because some people might want a shot from a different manufacturer. Minnesota is following the CDC's recommendations and has ample supplies of vaccine, Gov. Tim Walz said in a statement.

Most long-term care residents in Minnesota received the Moderna vaccine, so the announcement applies to a group that's been particularly hard-hit by COVID-19. Shots should begin within the next week or two at long-term care facilities operated by St. Louis Park-based St. Therese, said Lisa Kalla, the group's chief operating officer. Residents likely will receive boosters that are the same brand as their original immunizations.

"The only time I could see us deviating from that plan is if one of [the vaccines] wasn't available and our residents or staff … wanted to go outside of the current vaccination that they had," Kalla said. "I think it's more comfortable for residents just because they know what to expect."

A lot of the booster talk in Minnesota on Friday was about the chance to mix brands.

Julie McGuire, 63, of White Bear Lake says she was happy with the "one-and-done" nature of her J&J vaccine this spring and believes it helped keep her out of the hospital when she had a breakthrough infection in August — her second COVID illness in less than a year. But McGuire has been persuaded by recent reports about stronger protection with Moderna. With an immune system that's suppressed by a medicine she takes for rheumatoid arthritis, McGuire doesn't want to risk a third strike by the pandemic virus.

"I like the mix-and-match approach," she said.

Many J&J recipients likely will switch because, while all three vaccines are highly effective at preventing hospitalizations and deaths, "the perception out there amongst patients as well is that the J&J vaccine is maybe not as effective in preventing mild disease or COVID illness to begin with," said Dr. Lori Bethke, the chief medical officer at Entira Family Clinics in the east metro.

Preventing mild illness isn't the point of the vaccines, Bethke added, but it's important to patients who don't want to step out of their lives for 10 days under quarantine.

The ability to mix and match boosters gives clinics more flexibility in administering the vaccine, said Dr. Abraham Jacob, the chief quality officer at M Health Fairview. At NorthPoint Health and Wellness Center in Minneapolis, Dr. Paul Erickson said he already had one J&J patient walk in Friday asking for a different brand of booster.

"Our call centers, they've been getting calls like crazy today in terms of demand for the booster," Erickson added.

Preliminary results from an ongoing study suggest J&J vaccine recipients might see an even bigger antibody boost by switching brands, doctors noted Thursday during a meeting of CDC's Advisory Committee on Immunization Practices (ACIP).

Committee members said mixing could alleviate concerns about the very small risk of rare blood clots, particularly in women under 50, with the J&J vaccine. If they got J&J the first time, women in that age group might now boost with Pfizer or Moderna, said Dr. Helen Keipp Talbot of the Vanderbilt University School of Medicine.

Similarly, younger men could opt for J&J boosters if they started with the Pfizer or Moderna vaccines, which carry a very small risk in that age group of a heart problem called myocarditis, Talbot said during Thursday's ACIP meeting.

The idea makes sense, said Poland of Mayo Clinic, because it improves the risk-benefit ratio. What's still not clear with boosters, he added, is the timeline for giving them to people with breakthrough cases.

Not all clinics Friday were providing Moderna boosters because the shots are administered with just half the usual dose. Clinics need to adjust the process of administering doses that are drawn from multi-dose vials so they're careful not to waste doses, said Dr. Kevin Best, vice president of medical operations for primary care at Allina Health System. He urged patients to not feel like there's a time crunch.

"When you get the opportunity, go ahead and do it, but don't be concerned that if you're eligible for a booster you're particularly vulnerable," Best said.

The Minnesota Department of Health says while it will be important to get a booster shot, only get it when it is recommended, not earlier. A booster given too early may not be as effective at increasing protection.

CVS Health rolled out the new boosters in stores across the country on Friday, including at a location in Plymouth. A pharmacist who came out of retirement during the pandemic to help with the vaccine drive administered more than 20 booster shots, said Ashlee Slocum, the CVS Health district leader.

Each CVS store makes only one vaccine brand available at a time, so the ability to mix and match means that any one store can "take care of the booster for all of those eligible populations," Slocum said.