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Complete Guide to COVID-19 Booster Shots

Everything you need to know about getting an extra dose of the Pfizer, Moderna or J&J vaccine

vials of covid booster shots with an illustration of cells

CA-SSIS / Getty Images

En español     

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 — “with nearly 100 million doses in the field for immediate use.” 

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, which experts say can strengthen the body's immune response against the highly contagious delta and omicron variants.

Here’s what you need to know about getting a booster from Pfizer-BioNTech, Moderna or Johnson & Johnson before rolling up your sleeve.

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.

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. More than 245 million Americans have received at least one dose of a COVID-19 vaccine, and so far, no long-term side effects have been detected, the CDC says.

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.

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.

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 these events are rare and people usually recover quickly with medical care and rest.

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, based on new guidance from the FDA and CDC.

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.  

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. 

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.

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.

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.

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 Pfizer or J&J, that is an option, based on new guidance from the FDA and CDC.

Preliminary results from a federally funded study show that mixing and matching vaccine boosters can produce a higher level of antibodies, which is one measure of immune response, and no safety concerns were identified.  

Giving the green light for people to mix and match the products also makes getting the booster more convenient, especially in areas where options may be limited. However, if you’re thinking of mixing up your booster, it’s a good idea to talk to your doctor first, experts say.


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Johnson & Johnson  

Johnson & Johnson’s vaccine 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. 

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.

Preliminary results from a federally funded study show that mixing and matching vaccine boosters can produce a higher level of antibodies — especially among J&J vaccine recipients who were boosted with an mRNA vaccine. What’s more, no safety concerns were identified.

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.