Registered nurse Kelsey Trombley prepares a COVID-19 booster shot during a clinic last month at Cheshire Medical Center in Keene.

After months of being available for high-risk populations, COVID-19 booster shots have gotten the green light for all adults, federal health officials announced Friday.

Here’s a rundown of who can get a booster shot, why people need it and where, locally, to get it:

Who can now get a booster shot of the COVID-19 vaccine?

On Friday, the CDC said anyone 18 and older can get a booster shot, regardless of which vaccine they initially received.

Federal health officials hope this extension will eliminate any confusion on who can get the booster.

Will I receive the same type of vaccine I did before?

The CDC says people can choose which COVID-19 vaccine — by Pfizer-BioNTech, Moderna or Johnson & Johnson — they receive as a booster shot, regardless of which one they initially got. However, you can get the same vaccine if you’d prefer.

There’s been only one mix-and-match study on the vaccines available in the United States so far to examine the overall safety and efficacy of using a different COVID-19 vaccine for a booster than for the initial shot(s). The results showed doing so produced a safe immune response, similar to what was generated by an additional dose of the same first shot.

The National Institutes of Health study did not compare the different combinations, however, so it’s unclear if one combination of shots is better than another.

Why do people need a booster shot?

Dr. Aalok Khole, an infectious-disease physician at Cheshire Medical Center in Keene, said recent studies have shown the vaccines’ overall effectiveness begins to wane after a few months. A booster shot will help strengthen people’s protection against COVID-19.

Additionally, Khole said the booster shots’ extension to all adults will “bolster the fight for sure.”

“However, in my opinion, it is only part of the solution,” he said in an email. “The real push has to be to convince the unvaccinated to get their first shots and then complete the series.”

When should I get the booster shot?

The CDC recommends the booster shot be administered at least six months after receiving a second dose for people who initially got Pfizer or Moderna. Johnson & Johnson recipients can get their booster shot at least two months after inoculation.

What should I expect during and after getting my booster shot?

At your booster shot appointment, you’ll need to bring your COVID-19 vaccination card.

Afterward, the CDC says, you may experience side effects, just like after the initial shot(s). These are normal, the federal health agency reassures, as your body builds protection against the virus.

Side effects can include pain and swelling at the injection site, fatigue, chills and nausea.

Where can people get a booster shot?

Locally, Cheshire Medical Center is hosting two patient-only drive-thru clinics for Pfizer and Moderna boosters on Dec. 4 and 11 on its campus on Court Street in Keene. Appointments are required and can be made at myDH.org or by calling your provider, spokeswoman Heather Atwell said.

Patients of Monadnock Community Hospital in Peterborough can also get a booster through their primary-care provider, whom they should call to schedule an appointment, according to spokeswoman Laura Gingras.

As with the initial shots, appointments for a booster can also be made at vaccines.nh.gov, by calling the state’s hotline at 2-1-1 or by directly contacting your primary-care provider or local pharmacy. To find where boosters are available locally, go to www.vaccines.gov/search/.

Before making an appointment, people should consult with their health-care provider to determine if the booster shot is right for them, according to the CDC.

What will a COVID-19 booster shot cost me?

Like the initial doses of the vaccine, booster shots are free, regardless of insurance status.

Questions about the COVID-19 vaccines or anything else related to the viral disease can be answered at vaccines.nh.gov or by calling the state’s hotline at 2-1-1.

Olivia Belanger can be reached at 352-1234, extension 1439, or obelanger@keene-sentinel.com. Follow her on Twitter @OBelangerKS.