Home > Healthcare, Research & News > COVID-19 Vaccine: Understanding Additional Doses and Boosters

COVID-19 Vaccine: Understanding Additional Doses and Boosters

By Lisa Doggett
January 7, 2022

Don’t wear a mask… actually, wear a mask. Spray your groceries with bleach… no, that’s silly and unnecessary. Boosters are for everyone… no, boosters are only for older adults and those with chronic condition. No, we were right the first time—boosters are for everyone (age 12+).

I already struggle with dizziness related to MS. But keeping up with the ever-changing COVID-19 guidance really makes my head spin.

As a 2021-22 Vaccine Science Fellow with the American Academy of Family Physicians and an MS Warrior, I have been particularly interested in the vaccine recommendations for people living with MS. At first, I wondered if the vaccines would be safe for those of us taking disease-modifying therapies (they are). Then I wondered if they would work (they do). Now I’m trying to figure out how many vaccines I need, which type and when I should get them. It’s confusing, and the guidelines continue to evolve as we learn more.  So, here’s what we know now:

The Basics

  • The COVID-19 vaccines available in the U.S.—the two-dose Pfizer-BioNTech and Moderna (the “mRNA vaccines”), and the single-dose Johnson & Johnson Janssen (J & J) vaccine—are all safe for people with MS.
  • The mRNA vaccines are effective at preventing serious illness, hospitalization and death from COVID-19 and are now the preferred vaccines by the Centers for Disease Control and Prevention (CDC). However, those who are unable or unwilling to receive an mRNA vaccine will continue to have access to the J & J vaccine.
  • They are safe and effective in people with MS.
  • They are recommended for everyone ages 5 and up (however, the Pfizer vaccine is the only one authorized for kids 5-17).
  • For almost everyone, the benefits far outweigh any potential (very small) risks of getting a vaccine.
  • The vaccines are the most effective tool we have to beat COVID-19.


We also now know that vaccine effectiveness decreases over time, and as new surges and variants emerge—such as the Delta variant, and most recently Omicron—we have needed to redouble our efforts to protect as many people as possible. Extra vaccine doses are a critical part of that strategy.

Booster Shots: Recommended for Everyone to Reinforce Protection

The CDC now recommends booster vaccines for all everyone age 12 and older. Boosters are safe, and they serve as a way to reinforce prior vaccine-acquired immunity to COVID-19.

Additional Dose: Recommended for Immunocompromised to Ensure Adequate Protection

People who are immunocompromised need third doses of a Pfizer or Moderna shot not as a booster, but as an “additional dose.” If, like me, you take one of the disease-modifying drugs that can reduce your immune response to a vaccine, and you received two doses of an mRNA vaccine, you need an “additional dose” of the COVID-19 vaccine to help ensure adequate protection.

Check out the list of the applicable medicines that have been associated with reduced or absent antibody response to the vaccine.

Booster vs. Additional Dose Timing

Below is a chart that details the timing of booster shots vs. additional doses, broken down by vaccine type and eligibility:

Click the image for a larger version.

As an example, if you finished the two-shot series of the Pfizer vaccine in October and are immunocompromised, you should get your “additional dose” now, rather than waiting the full five months for a booster; if you finished the two-shot series of the Moderna vaccine in the same scenario, you should get your “additional” dose now, rather than waiting the full five months for a booster. For Johnson & Johnson vaccine recipients, immunocompromised or not, a booster with an mRNA vaccine is now recommended at least two months after the initial J & J dose.

For now, nearly everyone with MS should do the following:

  1. If you’re not vaccinated, please get an mRNA shot as soon as possible. Misinformation is abundant, and I urge you to seek information from reliable sources, including the CDC and the Society. Vaccines will help protect you and everyone around you.
  2. Check out the Society’s website and talk to your healthcare provider for guidance on vaccine timing, depending on your MS medication, to enhance vaccine effectiveness.
  3. Urge everyone around you to get vaccinated. By doing so, they are helping to protect not only themselves, but you and everyone else they interact with.
  4. If you take certain disease-modifying therapies that compromise immune responses to vaccines, and it’s been 28 days since you finished a two-dose series (Pfizer or Moderna), don’t wait for a booster. Get an “additional dose” now or as soon as recommended by your doctor to ensure the best timing with your MS medication.
  5. If you are getting an additional dose of Moderna, ensure it’s the full dose not the booster dose, which is only a half dose.
  6. If you had a single Johnson & Johnson vaccine, you should get a “booster” with an mRNA COVID-19 vaccine two months after your first shot.
  7. If you don’t take a medicine that can reduce vaccine immunity and you received your second mRNA vaccine at least five months ago, you should get a “booster” with an mRNA COVID-19 vaccine.

Of course, we continue to face unknowns. When I saw my neurologist in early December, we talked about one of them: Will I need a fourth dose of the COVID-19 vaccine? I got my third dose of the Pfizer vaccine six months after my second dose, so does it count as an “additional dose” or a booster? Do I need another vaccine five months after my last shot (is your head spinning, too?)? 

At this point, CDC vaccine guidelines recommend boosters for people who are moderately or severely immunocompromised five months after the “additional dose.” But this guidance could change. At this time with all the information and risks available to us, my doctor and I have decided that I should get my booster shot five months after my additional dose.

Researchers continue to study how immunity to the disease changes over time. We don’t know if some of us will end up needing even more doses or maybe an annual vaccine, like the flu shot. We do know SARS-CoV-2, the virus that causes COVID-19, can mutate into new variants, and it may change enough to reduce vaccine effectiveness over time. Vaccine manufacturers are already working to modify existing vaccines to be more protective against emerging variants. As the virus changes, so will the recommendations for vaccines and potentially other safety measures.

Those of us with MS are used to living with uncertainty. We never know when we might have a flare or a bad day challenged by mobility issues, brain fog, fatigue or some bizarre new symptom we never could have imagined. We learn to cope, to live in the moment, to adjust expectations. With the COVID-19 pandemic, we’ve made further adaptations, and we know to expect the unexpected, the inevitability of change. Over the next few months, I urge you to stay in touch with your healthcare provider and follow evolving guidance from the Society and CDC to decide if and when you might need further vaccines. And do your best to harness that courage and strength that comes from battling MS as we enter a new year challenged by the pandemic that just won’t stop.

Editor’s Note: For more information on COVID-19 vaccines and MS, visit the Society’s coronavirus resources page. This blog was originally published on December 13, 2021 and was updated on January 7, 2022.

The National Multiple Sclerosis Society is proud to be a source of information on multiple sclerosis related topics. Unless otherwise indicated, the information provided is based on professional advice, published experience and expert opinion. However, the information does not constitute medical or legal advice. For specific medical advice, consult a qualified physician. For specific legal advice, consult a qualified attorney.

Lisa Doggett

Lisa Doggett, MD, MPH is a family physician, writer, and MS Warrior (diagnosed in 2009). She lives with her husband and two daughters in Austin, Texas. Learn more about her and her journey with MS at lisadoggett.com.

Related Posts

MS volunteer

A Story of Two Movements: The MS Community Honors Dr. King

Address racial disparities and inequities in the healthcare system that impede access to care, and ultimately, a cure, for MS.

Evusheld and MS

5 Things To Know About Evusheld

The U.S. Food and Drug Administration (FDA) has recently authorized Evusheld for use to prevent… Read More

unpredictable MS symptoms

Limits That Change

The tricky thing about MS and the symptoms is that you are not guaranteed that… Read More