Millions of fully vaccinated people in the U.S. are now officially eligible for a COVID booster shot, following approval from both the Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC). Recipients can even pick and choose between any of the three vaccines—Pfizer, Moderna, or Johnson&Johnson—no matter which vaccine they received initially. As a result, nearly 13 million people have already gotten an additional shot, according to the CDC, and several major pharmacies like Walgreens, CVS, and Walmart are offering boosters nationwide. But if you're planning to get your next shot at CVS, the pharmacy is warning customers to do one thing prior to coming in for it.

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CVS started administering booster shots to all eligible recipients at more than 9,800 pharmacy locations in all 50 states on Oct. 22, according to its website. But the pharmacy is strongly urging anyone looking to get their booster at a participating CVS location to make an appointment beforehand.

"Advanced scheduling is recommended for patients looking to receive a COVID-19 vaccine from a specific manufacturer to ensure that it is available at the clinic of their choice," CVS explains in the frequently asked questions section of its website.

You can either make an appointment at CVS.com or on the CVS mobile app, with both giving you the option to pick a specific time and location. "When scheduling an appointment on CVS.com, patients will be asked to provide the manufacturer and date of their last COVID-19 vaccine," the pharmacy notes.

While you're allowed to choose any of the boosters, you still have to be eligible for a booster shot in relation to your first vaccine series. If you initially received the Pfizer or Moderna vaccine, you're eligible for a booster if you are more than six months out from your second shot and fall into one of these categories: are 65 years old or older, 18-64 and at high risk for severe COVID due to underlying conditions, or 18-64 and at high risk due to occupational or institutional exposure. On the other hand, all Johnson&Johnson recipients at least two months out from their shot are eligible for a booster.

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Currently, no CVS locations are administering the Johnson&Johnson booster, according to its website. In early August, the pharmaceutical chain stopped offering the Johnson&Johnson single-dose vaccine in its pharmacies, according to CNBC. From that point on, this vaccine has only been offered at some of CVS' MinuteClinic locations in 25 states and Washington, D.C., covering only about 10 percent of the company's retail locations.

CVS says that Johnson&Johnson recipients wanting either a Moderna or Pfizer booster can get their shot at one of its pharmacies, however. It is still advised that you make an appointment, as the specific mRNA booster you are looking for might not be administered at certain locations.

"At this time, each participating CVS Pharmacy is offering either the Pfizer-BioNTech or Moderna vaccine, not both," the pharmacy states on its website.

CVS has been a major player in the fight against COVID, administering vaccines since they were first authorized in late 2020. According to the pharmacy company's website, CVS Health has administered more than 34 million COVID vaccines over the last year. "The systems we've built and our deep experience in providing vaccinations allow us to play a leading role in administering booster shots to eligible populations," Troyen A. Brennan, MD, the chief medical officer of CVS Health, said in a statement on Oct. 22.

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