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Moderna COVID booster FAQ: You can mix and match with Pfizer after 5 months

Booster shots for Moderna's Spikevax vaccine have proven highly effective against omicron. You can now get boosted 5 months after a second shot of Pfizer.


New research shows the Moderna booster significantly increases protection against COVID and omicron.

Algi Febri Sugita/Getty Images
For the most up-to-date news and information about the coronavirus pandemic, visit the WHO and CDC websites.

The US Food and Drug Administration on Monday reduced the waiting period between the second shot of Pfizer's mRNA vaccine and a follow-up booster from six months to five, but retained the six-month waiting period for those who received initial vaccinations of Moderna's COVID-19 vaccine. That means you can get a Moderna booster five months after an initial Pfizer vaccination, but still need to wait six months after your second shot of Moderna.

Acting FDA Commissioner Janet Woodcock explained the distinctions in a media call on Monday, stating, "If you got J&J, you get a booster after two months. If you got Pfizer as your primary series, you can get a booster at five months or beyond. If you got Moderna, you can get a booster at six months or beyond."

As the omicron variant continues to be the dominant COVID-19 strain in the US, responsible for nearly 60% of new infections, research indicates that, without a third shot, vaccines are minimally effective against the highly contagious mutation. The good news is that research also indicates the Moderna booster is highly effective in increasing that protection.

Reports from December indicated antibodies in people who only got two doses of Moderna's mRNA vaccine were at least 50 times less effective at neutralizing the omicron variant. And a study released last week by the UK Health Security Agency found that 20 weeks after the second dose of an mRNA vaccine, protection against omicron decreased to just 10%.

With a third booster dose, though, that protection rocketed back up to 90%.

The UK report also strengthened the case for a Moderna booster, noting that protection against omicron was higher in those who received a Moderna booster after two Pfizer shots compared with those who received a third Pfizer shot. The Moderna booster was also slightly more effective than Pfizer for people who received two doses of the AstraZeneca vaccine.

But only one in three Americans have gotten a booster of a third dose of the Moderna or Pfizer COVID-19 vaccine or a second of Johnson & Johnson's. All three are effective in protecting against hospitalization and death, even from omicron, numerous studies have found.

People who are unvaccinated are 10 times more likely to be hospitalized if infected. With a federal vaccine mandate slated to start this month, the Biden administration expects even more Americans to get the jab.

Here's what you need to know about the Moderna booster, including doses, side effects and how to get a free ride to your vaccination appointment. For even more details, here's the latest on COVID-19 vaccines for kids, how you can soon get a free COVID-19 test kit and what to know about breakthrough infections

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How effective is the Moderna booster against the omicron variant?

On Dec. 20, Moderna President Stephen Hoge said early results demonstrated the company's COVID-19 vaccine booster increased "omicron-neutralizing antibodies" approximately 37-fold. For comparison, earlier this month Pfizer said its booster raises antibody levels 25-fold, offering "a sufficient level of protection" against omicron.

Early studies of omicron variant infections in the US support the idea that current vaccines offer weaker protection against the newest strain, especially for individuals who did not get a booster yet. 

CDC Director Dr. Rochelle Walensky said on Dec. 10 that, of the 43 earliest cases attributed to the omicron variant, 34 people had been fully vaccinated -- though only 14 of those patients had also received a booster. And five of the people who were boosted were infected less than 14 days after the third shot (before full protection kicks in).

What are the Moderna booster's possible side effects?

Side effects for Moderna's booster shot are similar to those from the two primary doses -- pain or swelling at the injection site, as well as fatigue, muscle pain, headache, fever, chills and nausea. The drugmaker said there is "a remote chance" that its COVID‑19 vaccine could cause a severe allergic reaction.

The good news is, according to the CDC, those who got the Moderna booster dose reported far fewer reactions than they did after the second dose of the vaccine. 

Will we need an annual COVID booster shot?

With vaccines appearing to offer waning protection and the continuing evolution of variants, Hoge said we will most likely need seasonal COVID boosters, much like we do with the flu, at least to protect those at high risk of infection.

The CDC updated its guidance to indicate that, starting in 2022, some immunocompromised people will be able to get a fourth COVID-19 booster shot. Israel, Germany and other nations are researching the efficacy of a fourth shot and Dr. Anthony Fauci, chief medical adviser to the president, said a fourth jab was "conceivable" in the US, too.

Is Moderna working on other COVID boosters?

Hoge said the company's current 50-microgram COVID booster gives "quite respectable" protection but Moderna is continuing to study an omicron-specific vaccine and a multivalent shot that could protect against multiple variants, including the alpha and delta strains. 

The firm also said a 100-microgram version of its current vaccine, Spikevax, appears to raise antibody protection 83-fold. Hoge said Moderna could have new versions of its vaccine ready early in 2022, but is not yet planning to ask the CDC and US Food and Drug Administration to amend its booster authorization for the 100-microgram trial version of Spikevax.

When can I get a COVID-19 vaccine booster shot?

On Monday, the FDA cut the waiting period between the second dose of an mRNA vaccine, like Moderna's shot, and a booster from six months to five. (Some countries, including Germany and South Korea, have reduced the waiting time down to three months.) 

The CDC and other health authorities are now urging people to get boosters as soon as they're eligible, to keep the immune response against omicron, delta and other coronavirus variants of concern as strong as possible. Moderna's mRNA vaccine booster has been approved for healthy Americans ages 18 and up. The FDA on Monday approved giving a booster of Pfizer-BioNTech's vaccine, Comirnaty, to kids as young as 12 and to those 5 and up with compromised immune systems or certain other health conditions.

Last month, President Joe Biden outlined a plan to contact the 64 million people on Medicare and AARP's 38 million members about getting a booster. Nationwide pharmacy chains like Walgreens, CVS and Rite Aid are also contacting customers who got a vaccine at their stores when it's time to schedule a booster.

Can people who are pregnant get a booster shot?

COVID-19 booster recommendations apply to all people 18 years and older, including pregnant women: "People who are pregnant or recently pregnant are more likely to get severely ill with COVID-19 compared with people who are not," the CDC website says.  

While there is no evidence that getting vaccinated decreases fertility in women or men, a recent study linked COVID-19 infection in pregnant women to a higher risk of stillbirth

Is the Moderna booster shot a full third dose of the vaccine?

The Moderna booster is a half dose of the same vaccine used in its first two full shots. The goal is to top up the formula and reinforce the body's immune response against the virus and its variants. While the first two shots of the Moderna vaccine were each 100 micrograms, the booster is a 50-microgram dose.

Moderna said a 100-microgram version of its current vaccine, Spikevax, appears to raise antibody protection 83-fold but it is not yet planning to ask the CDC or FDA to approve the more potent booster.

Moderna is also working on a combination shot that contains this year's flu vaccine and its COVID-19 booster vaccine, but that's not available right now.


Moderna's booster shot is currently half the size of a full dose.

Sarah Tew/CNET

How do I know which pharmacies have Moderna booster shots available?

Boosters are available at roughly 80,000 locations across the US, including over 40,000 pharmacies. Some 90% of Americans have a vaccine site within five miles of where they live.

free service backed by the CDC sends you information on vaccine sites when you text your ZIP code to this number: 438829. The response will show you COVID-19 vaccine locations in your area, along with the brands they carry for certain age groups, for instance, Moderna 18+. This can save you from having to call around, or show up to an appointment to find that your booster of choice isn't available. The text message also offers a shortcut to make your appointment right from your phone screen. 

In addition, you can check to see which vaccines are available where, or call 800-232-0233 for additional vaccine information.

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Who can get a Moderna booster shot right now?

On Jan. 3, all US adults 18 and older became eligible to receive COVID-19 booster shots if it's been at least five months since they've received a 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, even if that means mixing and matching vaccine boosters (more below). The CDC's recommendation of mRNA vaccines -- Moderna or Pfizer -- also applies to booster shots.


Moderna's booster shot is free of charge for all adults.

Sarah Tew/CNET

Is it safe to mix and match vaccine and booster brands?

Yes. The FDA has authorized mixing COVID-19 boosters, which in the US means Moderna and Pfizer. Any adult 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, if you qualify and it's been six months or longer since your second shot.

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.

Is the Moderna COVID-19 booster shot still free?

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 provide your insurance card information, including your name, date of birth and membership number. But you will not be charged for your COVID-19 vaccine or booster shot.

How can I get a free ride to get my vaccination booster appointment?

Lyft and Uber are offering free rides for some people who need them. An easy way to access those links for more information is through the text feature above. You can also go to or call Uber at 855-921-0033.

What does the Moderna booster shot do?

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

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-19 infections than those vaccinated this year, suggesting the need for a booster to maintain high levels of protection.

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.

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.