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An illustration of a medical disposable syringe filled with the COVID-19 vaccine.

Booster shots for the COVID-19 vaccine are on ongoing discussion in the U.S., and now it’s expected that eligible Americans will be able to get booster shots for any of the three available vaccines.

If you’re at high risk for severe COVID-19, you can already receive a booster of the Pfizer COVID-19 vaccine in the U.S. six months after your primary Pfizer series.

An FDA advisory committee has also recommended booster shots for the Moderna and Johnson & Johnson vaccines, which could get authorization and start rolling out to eligible Americans later this week. (Although it’s not required to, the FDA typically adheres to the recommendations of its advisory committees.)

Late last week, the panel of FDA advisers unanimously recommended that a booster dose of the Moderna COVID-19 vaccine (half the dose of the initial shots) be given at least six months after the initial two-dose regimen to people 65 years and older, those 18 to 64 who are at high risk of severe COVID-19, and adults whose work or institutional exposure puts them at high risk for COVID-19 — mirroring the recommendations for the Pfizer booster, per NPR.

Meanwhile, the Johnson & Johnson vaccine booster was also given unanimous approval last week, which will likely allow all 15 million people who received the initial dose to get a second shot at least two months later, per the New York Times. This is a different recommendation than that for Pfizer and Moderna. For those vaccines, the booster is limited to high-risk groups, while a booster for Johnson & Johnson would be available to everyone who received it originally.

The agency is also considering recommending the option of a Pfizer or Moderna vaccine booster option for Johnson & Johnson recipients — known as a “mix-and-match” approach.

When the FDA grants an emergency use authorization (EUA) for boosters based on the committee’s recommendations for the Moderna and Johnson & Johnson boosters, the U.S. Centers for Disease Control and Prevention (CDC) will then determine who is eligible for the doses.

Who Is Considered High-Risk and Should Get Pfizer COVID-19 Booster?

 According to the FDA, the EUA for a booster dose of the Pfizer vaccine applies to the following groups. The same groups would likely qualify for the Moderna booster.

  • Individuals 65 years of age and older
  • Individuals 18 through 64 years of age at high risk of severe COVID-19
  • Individuals 18 through 64 years of age whose frequent institutional or occupational exposure to SARS-CoV-2 puts them at high risk of serious complications of COVID-19 including severe COVID-19 (for instance, health care workers, teachers and daycare staff, grocery workers, and those in homeless shelters or prisons)

There are several factors that can put you at higher risk of COVID-19, including underlying medical conditions, according to the CDC. These conditions include:

  • Cancer
  • Chronic kidney disease
  • Chronic lung disease
  • Dementia or other neurological conditions
  • Diabetes (type 1 or type 2)
  • Down syndrome
  • Heart conditions
  • HIV
  • Immunocompromised state
  • Liver disease
  • Overweight and obesity
  • Pregnancy
  • Sickle cell disease and thalassemia
  • Smoking
  • Transplant recipients
  • Stroke
  • Substance use disorders

Note that certain people with some of these conditions already qualified for a third COVID-19 vaccine dose, including cancer, transplant recipients, and the immunocompromised. Read more below about the difference between getting a booster and getting a third dose.

“I do recommend that high-risk groups, as designated by the CDC’s Advisory Committee on Immunization Practices, who received Pfizer vaccinations get a booster six months post their second dose,” says infectious disease physician Amesh A. Adalja, MD, a Senior Scholar at Johns Hopkins Center for Health Security. “There is clear evidence that in the rare instances in which breakthrough infections result in hospitalizations or death, individuals who are above the age of 65 are overrepresented.”

While scientific advisors on the CDC’s committee voted to recommend these booster shots for older adults and those who have underlying medical conditions (based on the severity of their condition and individual risk), they stopped short of recommending them for individuals based on their occupation, per the New York Times.

The CDC committee noted that there isn’t strong evidence to support that this group experiences higher rates of severe disease if they are vaccinated, reports Time. However, in a rare move, CDC Director Rochelle Walensky overruled the agency’s advisory panel and added the booster recommendation for people whose occupations put them at risk of infection.

Who Will Likely Be Able to Get Moderna and Johnson & Johnson Vaccine Boosters?

The specifications for Pfizer boosters are mirrored in the current recommendations for the Moderna booster shot, which the FDA advisory panel has recommended for people 65 years and older, those 18 to 64 who are at high risk of severe COVID-19, and adults whose work or institutional exposure puts them at high risk for COVID-19.

The panel has discussed but has thus far not supported Pfizer and Moderna boosters for the general population ages 18 to 65, per NPR.

On the other hand, because the Johnson & Johnson vaccine has been shown to have lower efficacy than the Pfizer and Moderna shots, the FDA committee recommended that everyone who received the Johnson & Johnson vaccine receive an additional shot. Although this is being called a booster, some experts argue that the Johnson & Johnson vaccine should have included two doses (separated by about two months) from the start, per The New York Times.

Mix-and-Match Boosters for the Johnson & Johnson Vaccine

It’s expected that regulators will soon consider if Johnson & Johnson recipients should be able to get boosters of an mRNA vaccine for a stronger response. Preliminary findings have shown that Johnson & Johnson recipients who receive a Moderna vaccine booster see a 76-fold increase in antibody levels within 15 days, compared with just a fourfold rise with a Johnson & Johnson booster, per an October 2021 pre-print study posted on MedRxiv. A Pfizer booster raised antibody levels by 35-fold. That said, the trial only looked at antibody levels, which don’t show the full picture of how vaccines can protect individuals.

Booster Shot vs. Third Dose: What’s the Difference?

Generally, the only difference is the purpose of the dose. (However, in the case of the Moderna booster shot, the dose is also different. The booster dose is half that of the original dose.)

In August, the FDA adjusted the emergency use authorizations (EUAs) for the Pfizer and Moderna vaccines to allow for an extra dose to be given to certain immunocompromised individuals. The amendment applies to solid organ transplant recipients or those diagnosed with conditions considered to have an equivalent level of immunocompromise.

This includes many people with inflammatory or autoimmune conditions who take immunosuppressant or immunomodulating medications.

In this case, you should wait at least 28 days between your second and third doses, but your doctor will be able to best determine the right timing of vaccination, per the CDC.

“The purpose of a third dose is to try to accomplish in these individuals what two doses accomplished in everybody else,” David Aronoff, MD, Director of the Division of Infectious Diseases at Vanderbilt University School of Medicine in Nashville, Tennessee, previously told CreakyJoints. “It’s essentially saying, ‘Because your immune system is suppressed, you may not respond normally to this vaccine. So for you, the normal regimen is a three-dose regimen, not a two-dose regimen.’”

Booster shots, on the other hand, are meant to increase immunity when antibody levels wane over time. In the case of the recent EUA for Pfizer COVID-19 vaccine, the booster shots are being focused on those who may need extra protection the most.

The Moderna vaccine booster differs from the Pfizer and Johsnon & Johnson vaccine boosters in that its COVID-19 vaccine booster shot is a half-dose of the initial shot. It contains only 50 micrograms of mRNA, compared to 100 micrograms in each initial shot, per NPR.

During the CDC committee meeting for the Pfizer vaccine, scientists showed models indicating that even if booster shots slightly increased protection against hospitalization, they could prevent more than 2,000 hospitalizations per million doses given, according to the New York Times.

Will Immunocompromised People Need a Third Dose AND a Booster?

If you are immunocompromised and got a third dose of the COVID-19 vaccine, it’s too early to say whether you may also need a booster (technically a fourth dose) down the line. It’s possible in the future, but there is not yet data to recommend this. The guidance surrounding the COVID-19 vaccine is constantly evolving as more research emerges.

“Most likely, a fourth vaccine dose will be needed in immunocompromised patients, but we’re waiting on data from studies,” Daniel Arkfeld, MD, a rheumatologist with Keck Medicine of USC, told CreakyJoints previously. “I expect that will probably happen.”

Which Vaccines Will Be Given as a Booster?

This is where things get a little confusing.

  • If you’re immunocompromised (due to, say, taking immunosuppressant medications) both the Moderna and Pfizer vaccines are available as a third dose, at least 28 days after you received your second dose.
  • If you’re high-risk for severe COVID-19 but not immunocompromised (due to, say, obesity or diabetes), so far only the Pfizer COVID-19 is available as a booster in the U.S. The Pfizer booster is recommended six months after you received your second dose. Booster doses for the Moderna and Johnson & Johnson vaccines will likely be available later this month, but they are not fully authorized yet.

Does Your Booster Have to Be the Same as Your First Two Vaccines?

Mixing and matching vaccines (say, getting Moderna as a first dose and Pfizer as a second dose) has been used in Europe and other places, particularly in the case of shortages, according to Yale Medicine. Current public health recommendations in the United States suggest sticking with one type of mRNA vaccine for both doses. However, switching is permitted for the third dose for immunocompromised people if necessary.

This may change to allow for more flexibility after the FDA and CDC review more recent data. It may be the case that mixing and matching vaccines is permitted but less of an issue when it comes to the Pfizer and Moderna vaccines, because the effectiveness is similar.

Where mixing and matching may become more critical is with the Johnson & Johnson vaccine. Regulators will soon consider if Johnson & Johnson recipients should be able to get boosters of an mRNA vaccine. Early research shows this may lead to a stronger immune response compared to a Johnson & Johnson booster

Where Do You Get the Booster Dose?

If you’re not sure whether you qualify for a COVID-19 booster based on your underlying medical conditions, talk to your doctor to determine if you need a booster dose.

Pfizer booster shots should be available where vaccines are already being offered, including pharmacies, health departments, clinics, and some doctor’s offices. This will likely be the case for Moderna and Johnson & Johnson booster shots once they’re available, too.

What Should I Tell My Loved Ones Who Are Eligible?

If you’re immunocompromised because of an inflammatory or autoimmune condition and already received your third COVID-19 vaccine dose, you’re likely doing many things to bolster your protection and reduce your risk of getting sick. If you have people in your life who are now eligible for a COVID-19 booster shot, you should encourage them to get one — to protect themselves, of course, but also to help keep you safe too.

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Atmar RL, et al. Heterologous SARS-CoV-2 Booster Vaccinations – Preliminary Report. MexRxiv. October 13, 2021. https://doi.org/10.1101/2021.10.10.21264827.

Coronavirus (COVID-19) Update: FDA Authorizes Additional Vaccine Dose for Certain Immunocompromised Individuals. U.S. Food & Drug Administration. August 12, 2021. https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-additional-vaccine-dose-certain-immunocompromised.

FDA Authorizes Booster Dose of Pfizer-BioNTech COVID-19 Vaccine for Certain Populations. U.S. Food & Drug Administration. September 22, 2021. https://www.fda.gov/news-events/press-announcements/fda-authorizes-booster-dose-pfizer-biontech-covid-19-vaccine-certain-populations.

Hensley S. Experts recommend that FDA should authorize Moderna COVID vaccine booster. NPR. October 14, 2020. https://www.npr.org/sections/health-shots/2021/10/14/1046079675/experts-recommend-that-fda-should-authorize-moderna-covid-vaccine-booster.

Interview with Amesh A. Adalja, MD, a Senior Scholar at Johns Hopkins Center for Health Security

Interview with Daniel Arkfeld, MD, a rheumatologist with Keck Medicine of USC

Interview with David Aronoff, MD, Director of the Division of Infectious Diseases at Vanderbilt University School of Medicine in Nashville, Tennessee

Interview with  S. Louis Bridges, Jr., MD, PhD, Physician-in-Chief and Chief of the Division of Rheumatology

Joint Statement from HHS Public Health and Medical Experts on COVID-19 Booster Shots. CDC Newsroom. U.S. Centers for Disease Control and Prevention. August 18, 2021. https://www.cdc.gov/media/releases/2021/s0818-covid-19-booster-shots.html.

LaFraniere S, et al. F.D.A. Panel Unanimously Recommends Johnson & Johnson Booster Shots. The New York Times. October 15, 2021. https://www.nytimes.com/2021/10/15/health/johnson-johnson-vaccine-booster.html.

Mandavilli A, et al. The C.D.C. chief overruled her own agency’s panel and recommended Pfizer boosters for workers at risk. The New York Times. September 23, 2021. https://www.nytimes.com/2021/09/23/health/pfizer-booster-cdc-fda-authorize.html.

Park A. CDC Panel Outlines Who Should Get Pfizer-BioNTech COVID-19 Booster Shots, And Who Should Wait. Time. September 23, 2021. https://time.com/6101259/cdc-pfizer-booster-shot/.

People with Certain Medical Conditions. COVID-19. U.S. Centers for Disease Control and Prevention. August 20, 2021. https://www.cdc.gov/coronavirus/2019-ncov/need-extra-precautions/people-with-medical-conditions.html.

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