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Complete Guide to COVID-19 Booster Shots

Everything you need to know about getting an extra dose — or two — of the vaccines

COVID booster shots are now available for many people.
CA-SSIS / Getty Images

The Centers for Disease Control and Prevention (CDC) issued a statement on Dec. 16 recommending Pfizer’s and Moderna’s mRNA COVID-19 vaccines over Johnson & Johnson’s single-shot product. However, “individuals who are unable or unwilling to receive an mRNA vaccine will continue to have access to Johnson & Johnson’s COVID-19 vaccine,” the CDC says. The majority of vaccinated Americans have been vaccinated with the mRNA vaccines, and the CDC says the supply of them is abundant.

     

Booster shots for all three COVID-19 vaccines have received the green light from federal health officials, and millions of Americans are eligible for the extra dose — some are now eligible for two. 

Experts say boosters can strengthen the body’s immune response against the highly contagious omicron variant and its fast-spreading subvariant, BA.2, and prevent some of the worst outcomes of a coronavirus infection. Unvaccinated individuals were 21 times more likely to die than their boosted peers during the height of the omicron surge, federal data show. And in the 65-plus age group, hospitalizations were nine times higher in unvaccinated individuals, compared to those who had been vaccinated and boosted. Here’s what you need to know about getting a booster from Pfizer-BioNTech, Moderna or Johnson & Johnson (J&J) before rolling up your sleeve.

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Pfizer

Pfizer’s mRNA booster has been available to millions of Americans since Sept. 24, as it was the first of the three COVID-19 vaccine boosters to pass regulatory hurdles from the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC).  

Who qualifies?

  • People 12 and older who were vaccinated with two doses of Pfizer’s COVID-19 vaccine at least five months ago.
  • Adults 18 and older who were vaccinated with two doses of Moderna’s COVID-19 vaccine at least five months ago. 
  • Adults 18 and older who were vaccinated with Johnson & Johnson’s single-shot COVID-19 vaccine at least two months ago.

Adults 50 and older can receive a second booster of Pfizer-BioNTech’s product at least four months after receipt of a first booster dose of any authorized or approved COVID-19 vaccine. So can people 12 and older “who have undergone solid organ transplantation, or who are living with conditions that are considered to have an equivalent level of immunocompromise,” the FDA says.

What are the side effects?

Pfizer’s booster is the same formulation and dosage as the first two shots in the series. And clinical trial data shows the side effects from it are similar to those many experienced the first time around, the most common being:

  • Injection site pain
  • Fatigue
  • Headache
  • Muscle pain
  • Chills

These symptoms are usually mild to moderate in severity and typically resolve in a few days.

What are the rare reactions associated with this vaccine?

More serious side effects can occur but are rare. Anaphylaxis, a severe allergic reaction, is one example. A small number of people have experienced this after getting vaccinated against COVID-19. However, anaphylaxis can happen after any vaccination, and vaccine providers should be able to treat it quickly.   

Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the sac that surrounds the heart) have been linked to the mRNA vaccines (Pfizer and Moderna). Cases have mostly been reported in males under 30, more often after the second dose. Symptoms — chest pain, shortness of breath, feelings of having a fast-beating, fluttering or pounding heart — can pop up several days after vaccination. Experts stress that these events are rare and people usually recover quickly with medical care and rest, but it’s important to know the signs. 

Can I get boosted with another brand?

Yes. If you are 18 or older and qualify for Pfizer’s booster but don’t have access to it or want to get a booster from Moderna or J&J, that is an option, though health officials recommend the mRNA vaccines (Pfizer and Moderna) over J&J’s product.  (People age 12 through 17 can only get boosted with Pfizer at this time.) 

Preliminary results from a federally funded study show that while boosters from all three manufacturers (Pfizer, Moderna and J&J) enhance antibody levels, getting boosted with a vaccine from a different manufacturer can have a more pronounced effect on immune response. What’s more, the study showed no new or concerning side effects from mixing and matching.

Need help getting a COVID-19 vaccine or booster?

Visit vaccines.gov or call 800-232-0233 (TTY: 888-720-7489) for assistance in English, Spanish, and many other languages.

If you’re thinking of mixing up your booster, it’s a good idea to talk to your doctor first, says Mohammad Sobhanie, M.D., an infectious disease expert at the Ohio State University Wexner Medical Center. “I think it’s incredibly important that you have these conversations with your primary care physician so that they can give you the best advice out there based on your medical conditions,” he says.

Moderna

Moderna’s booster, another mRNA vaccine, got the go-ahead from health officials on Oct. 21.

Who qualifies?

  • Adults 18 and older who were vaccinated with two doses of Pfizer’s COVID-19 vaccine at least five months ago.
  • Adults 18 and older who were vaccinated with two doses of Moderna’s COVID-19 vaccine at least five months ago. 
  • Adults 18 and older who were vaccinated with Johnson & Johnson’s single-shot COVID-19 vaccine at least two months ago.  

Adults 50 and older can receive a second booster of Moderna’s product at least four months after receipt of a first booster dose of any authorized or approved COVID-19 vaccine. So can people 18 and older who have certain conditions that compromise their immune systems, including people who have undergone solid organ transplantation.  

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What are the side effects? 

Moderna’s booster shot is different from Pfizer’s and J&J’s boosters because it is half the dose (50 micrograms) of the initial vaccine.

Still, studies show the side effects of this smaller dose are similar to those many experienced after shots one and two in the series, the most common being:

  • Injection site pain
  • Fatigue
  • Headache
  • Muscle pain
  • Joint pain

Swollen lymph nodes in the underarm were observed more frequently following Moderna’s booster dose than after the primary two-dose series, according to the FDA.

What are the rare reactions associated with this vaccine?

Just like Pfizer’s vaccine, Moderna’s product has also been linked to myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the sac that surrounds the heart). These cases are rare and have mostly occurred in young men (30 and under) after the second vaccine dose.

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Other serious side effects can occur but are rare, including anaphylaxis, which is a severe allergic reaction that can happen after any vaccination.

Can I get boosted with another brand?

Yes. If you qualify for Moderna’s booster but don’t have access to it or want to get a booster from another approved or authorized brand, that is an option. Health officials say the mRNA vaccines (Pfizer and Moderna) are preferred in most booster situations, but J&J’s product is also available to some. 

However, if you’re thinking of mixing up your booster, it’s a good idea to talk to your doctor first, experts say.

Johnson & Johnson  

Johnson & Johnson also has a booster shot available, although the CDC recommends the mRNA vaccines from Pfizer and Moderna over J&J’s product.

Who qualifies?

J&J’s booster is available to:

  • Adults 18 and older who had the single-shot J&J vaccine, also known as the Janssen vaccine, at least two months ago.
  • Adults 18 and older who were vaccinated at least five months ago with two doses of Pfizer.
  • Adults 18 and older who were vaccinated at least five months ago with two doses of the Moderna vaccine.

And on March 29, the CDC announced that adults who received a primary vaccine and booster dose of J&J’s vaccine at least four months ago can now receive a second booster dose using an mRNA COVID-19 vaccine. 

What are the side effects?

Just like with Pfizer and Moderna, some clinical trial participants reported mild to moderate side effects after the J&J booster, the most common being:

  • Injection site pain
  • Fatigue
  • Headache
  • Muscle pain
  • Nausea

What are the rare reactions associated with this vaccine?

A rare but serious blood clotting disorder called thrombosis with thrombocytopenia syndrome (TTS) has been associated with the J&J vaccine. Fifty-four cases of the condition were confirmed as of August out of about 14 million doses administered; nine people have died from it. Young women in their 30s and 40s are most at risk. After reviewing evidence of the adverse event, the CDC decided on Dec. 16 to recommend Pfizer’s and Moderna’s vaccines over J&J’s product. J&J’s vaccine, however, is still available to those who are “unable or unwilling” to get vaccinated with Pfizer or Moderna. 

The CDC and FDA are also monitoring reports of Guillain-Barré Syndrome in people who have received the J&J vaccine. This rare disorder can lead to muscle weakness and sometimes paralysis, from which most people recover. There have been around 268 preliminary reports of Guillain-Barré identified out of more than 17 million J&J vaccine doses administered; most have been in men 50 and older.

Can I get boosted with another brand?

Yes. If you had J&J’s vaccine at least two months ago and want to get a booster from either Pfizer or Moderna, that is an option and, in fact, is recommended.

A new study published by the CDC found that vaccine effectiveness against emergency department and urgent care visits for COVID-19 was 24 percent after one J&J dose and 54 percent after two J&J doses, but was 79 percent after one J&J dose and one mRNA dose. One J&J dose plus one mRNA dose was 90 percent effective at preventing hospitalization for COVID-19; two J&J shots were 78 percent effective. 

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Getting a booster? What to know:

  • Just like with the initial COVID-19 vaccines, there are no out-of-pocket costs to get a booster shot; no insurance or ID is required.
  • You can find booster shots where you find the COVID-19 vaccines — pharmacies, doctor’s offices, community health clinics, etc. You may need an appointment, so check on the details.
  • It’s a good idea to call ahead of time to confirm the location has the booster brand you want to receive.
  • Bring your COVID-19 vaccine card so it can be updated to include your booster. Lost it? Here’s some advice on what to do.
  • You may experience some mild to moderate side effects after your booster — the most common are fatigue and pain at the injection site.

However, if you’re thinking of mixing up your booster, it’s a good idea to talk to your doctor first, experts say.

Editor's note: This story has been updated to reflect new information.

Rachel Nania writes about health care and health policy for AARP. Previously she was a reporter and editor for WTOP Radio in Washington, D.C. A recipient of a Gracie Award and a regional Edward R. Murrow Award, she also participated in a dementia fellowship with the National Press Foundation.

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