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Moderna COVID booster: What to know about the vaccine and new variant, side effects, CDC rules

If you're age 18 or older and it's been at least six months since your second shot, you're now eligible to get a Moderna booster dose.

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The Moderna booster is here. The CDC recommends you get one.

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For the most up-to-date news and information about the coronavirus pandemic, visit the WHO and CDC websites.

The new COVID-19 variant was just identified in South Africa last week, and Moderna said it's exploring three paths to protect against the mutated virus that could include creating a COVID-19 vaccine tailored specifically for the new virus strain early in 2022, if needed.

The new COVID-19 variant is raising alarm bells around the world with fears that the mutated virus could lead to a new surge of infections, much like the delta variant did over the summer.

If you're 18 years of age and older in the US, you now qualify for a Moderna booster shot. That goes for those fully vaccinated with the Pfizer, Moderna and Johnson & Johnson vaccines, too, because you can now mix and match vaccines from approved drug-makers. Authorization for the Moderna booster -- along with Pfizer and Johnson & Johnson booster shots and Pfizer vaccines for kids -- comes at a time when the deadly and contagious delta variant has a lock on the US and as the new omicron mutation emerges.

The COVID-19 vaccines have proven to be highly effective in preventing hospitalization, and those who are unvaccinated are 10 times more likely to be hospitalized if infected. With the federal vaccine mandates, the Biden administration aims to counter the surge and put pressure on anyone who hasn't been vaccinated. Antiviral drugs could also help.

Here's what you need to know about the Moderna booster, including its side effects. For more details, here's the latest on COVID-19 vaccines for kids, what to do if you lost your vaccination card, the difference between a booster and a third dose, and what to know about breakthrough infections

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What is Moderna doing with its COVID vaccine and booster for the new COVID-19 variant?

Scientists worry the new variant, named omicron, could spread more quickly than the now-dominant delta variant because of the number of mutations the new strain has.

Moderna Chief Medical Officer Paul Burton told the BBC the drug-maker is researching the effectiveness of its COVID-19 vaccine against the new variant discovered in South Africa late last week.

"Will we be able to neutralize it and control it and contain it with the current vaccines?" Burton asked about Moderna's response to the variant. "We should know in a couple of weeks from laboratory experiments."

Burton said Moderna has a three-part strategy to be ready for the mutated virus: Firstly, it's testing a 100-microgram dose of its booster to see if it provides better protection against the omicron variant. The Moderna booster authorized by the Centers for Disease Control and Prevention is a 50-microgram dose, half of what the CDC authorized for the first two shots of the Moderna vaccine. Secondly, it's testing a COVID-19 vaccine that could protect against several mutated strains of the coronavirus. And thirdly, the company is working on an omicron-specific booster vaccine. Burton said if Moderna needs to make a new vaccine modified for the variant, it could be available early in 2022.

All adults are now eligible for the Moderna booster dose

As of Nov. 19, all US adults -- those age 18 and older -- are eligible to get a booster shot of the COVID-19 vaccine. They qualify if it's been at least six months since they've received their second dose of either the Moderna or Pfizer vaccine. Those who received the Johnson & Johnson vaccine are eligible for a booster dose after two months. Adults are encouraged to get whatever booster dose is available to them, even if that means mixing and matching vaccine boosters (more below), in other words, getting a different booster shot than their original vaccination.

What about side effects of the Moderna COVID booster shot?

According to the US Centers for Disease Control and Prevention, those who got the Moderna booster dose reported fewer reactions than they did after the second dose of the vaccine. In its study, the CDC found 95% of those who got Moderna for the first round of vaccine shots chose Moderna for the booster dose.

Yes, it's safe to mix-and-match vaccine boosters

The US Food and Drug Administration has authorized mixing COVID-19 boosters, which in the US means Moderna, Pfizer and Johnson & Johnson. Anyone eligible for a booster can get any of the available brands of coronavirus vaccines. If you initially received Johnson & Johnson and it's been two months or longer since you received the initial dose, you'll be able to get the Moderna or Pfizer booster. If you received Moderna or Pfizer for your first two shots, you could pick any authorized vaccine available to you -- including J&J -- if you qualify and it's been six months or longer since your second shot.

What does the Moderna booster shot do?

A COVID-19 booster shot -- whether from Moderna, Pfizer or Johnson & Johnson -- tops off your immune response and guards against a breakthrough COVID-19 infection as the vaccine's effectiveness decreases over time.

Recent studies of the Pfizer and AstraZeneca vaccines show that their effectiveness can begin to wane after six months. Moderna said early data suggests that those who received the Moderna vaccine in 2020 are showing a higher rate of breakthrough COVID infections than those vaccinated this year, suggesting the need for a booster to maintain high levels of protection.

Is the Moderna vaccine booster the same as the original 2 COVID-19 doses?

Yes, almost. As with Pfizer's booster, the third Moderna shot will be the same vaccine as the first two doses, except it'll be a half dose. Moderna is also working on a combination shot that includes this year's flu vaccine and its COVID-19 booster vaccine, but that's not available right now.

Where can I get the Moderna booster shot?

According to the White House, boosters will be available at roughly 80,000 places across the country, including over 40,000 local pharmacies. Some 90% of Americans have a vaccine site within 5 miles of where they live. You can check Vaccines.gov to see which vaccines are available where, or call 800-232-0233 for vaccine information.

Is the Moderna COVID-19 booster shot free, or do I have to pay?

All booster shots will be free, regardless of immigration or health insurance status. However, depending on where you get your booster shot -- for example, at a local pharmacy -- you may be asked to log your insurance status. You may be asked to provide your insurance card information, including your name, date of birth and membership number. You will not be charged for your COVID-19 vaccine or booster shot.

Will I need a fourth COVID booster shot?

The CDC updated its guidance to say that next year, some immunocompromised people will be able to get a fourth COVID-19 booster shot. It's unclear if other groups will need to get a fourth dose at this time. 

For more on coronavirus treatments and vaccines, here's what we know about monoclonal antibody treatments, the new federal vaccine mandates and why some people may not want the shot.

CNET's Jessica Rendall contributed to this article.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.