COVID-19 Vaccine Information

Last updated Jan. 12, 2022

Booster shots have now been approved for all three of the COVID-19 vaccines available in the U.S. And the Centers for Disease Control and Prevention’s (CDC) new guidelines say that people who are fully vaccinated against the coronavirus can now mix and match their immunizations when seeking a booster shot.

But what does that mean, exactly? Is it better to stick with the same kind of vaccine you originally received, or are there situations in which it might be better to get a different one? And are the rules different for cancer patients in active treatment or for survivors who are immunocompromised?

We went to infectious diseases specialist and head of Internal Medicine David Tweardy, M.D., for answers. Here’s what he had to say.

How does the CDC define ‘mixing and matching,’ in this context? Is that option only for fully vaccinated people seeking a booster shot, or is it open to previously unvaccinated people, too?

In this context, it means getting a booster shot — or a supplementary dose of vaccine to bolster your body’s defense against the coronavirus — from a different manufacturer than the one which provided your original vaccination regimen. This applies no matter which type of vaccine you got first.

But anyone who is starting fresh needs to follow the CDC guidelines for initial vaccination, and receive either Johnson & Johnson’s Janssen single-dose shot, or both doses of a two-dose mRNA regimen from the same manufacturer (Pfizer/BioNTech or Moderna).

Why do we even need booster shots? Doesn’t being fully vaccinated confer the maximum amount of protection a person can have?

It does for a while, but over time, that protection wanes. And this is perfectly normal. Bodies are naturally very efficient and need to be able to respond to any number of infections, so they don’t want to waste resources maintaining the maximum level of defense forever against a pathogen they may or may not encounter.

But the number of COVID-neutralizing antibodies appears to drop significantly in fully vaccinated individuals after about eight months. And that increases the chance of breakthrough infections. So, waning protection is the main reason to get a booster shot. As long as the delta variant and/or omicron variant are still hanging around, it’s prudent to make every effort to maintain the highest levels of protection. And getting a booster shot is a good way to do that.

The other reason for booster shots is to protect ourselves against other variants. Pfizer and Moderna both began working on updated vaccines right away, in case they were needed against emerging strains. The thinking then was that we might need those in order to sustain high levels of neutralizing antibodies in people.

But it turns out that the original formulation is still very effective against both the alpha and delta variants. So, the manufacturers decided, “OK. Let’s just boost with the original.”

So, the booster shots are exactly the same as the original vaccines?

Yes, but with one exception: the Moderna booster only contains half the original dose.

There’s been a recognition that recipients of the Moderna vaccine saw their antibody levels decline more slowly than those who received the Pfizer or J&J vaccines. So, less vaccine was needed to build their levels back up to the desired amount.

There was also an acknowledgement that side effects tended to be more pronounced after the second shot in a two-shot series, so if a lower dose could do the job, it might also reduce the severity of any potential side effects.

Let’s say I got the single-dose J&J shot for my original vaccination. If I opt to get my booster dose from Pfizer or Moderna, does that mean I need two shots to be considered fully “boosted,” since two doses were needed initially to confer maximum protection?

No. No matter which vaccine you received initially, you will only need a single booster shot from any of the three manufacturers.

Is it better to stick with the same type of vaccine you originally got for the booster shot? Or is there some benefit to be gained by “switching horses,” so to speak?

It looks like the preferred way to go is to stick with the same vaccine. None of the data I’ve seen has shown the superiority of any particular combination of mixing and matching when it comes to efficacy.

What about cancer patients? Is there anything special they should know about mixing and matching booster shots?

The recommendation for cancer patients also is to stick with the same vaccine for their booster shot. In the case of the Pfizer or Moderna vaccines, the booster shot should be timed 5 months after their second dose, while for the J & J vaccine, it should be time at least 2 months after the single dose of this vaccine.

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If you’re a cancer patient who was fully vaccinated against COVID-19 before having a stem cell transplant or receiving a CAR T cell infusion, take note.

The Centers for Disease Control and Prevention (CDC) has issued a new recommendation for you — and it means starting all over again when it comes to COVID-19 vaccination.

New guidance adopted to protect stem cell transplant and CAR T cell therapy patients

The CDC’s new recommendation states that anyone who was fully vaccinated against COVID-19 before receiving a stem cell transplant or CAR T cell therapy should begin the vaccination process again from scratch — ideally, three months after either procedure.

“We know that stem cell transplant patients and CAR T cell recipients are particularly immunocompromised, because they get high-dose chemotherapy to suppress their immune systems,” says Roy Chemaly, M.D., MD Anderson’s Chief Infection Control Officer. “So, if they got vaccinated prior to that, then they’re going to lose that protection.”

New guidance applies only to a small group of patients

The new guidance applies only to patients who received a stem cell transplant or CAR T cell therapy after being vaccinated for COVID-19. But it’s critical for anyone to whom the recommendation does apply to follow it quickly — and to get re-vaccinated as soon as possible.

“Even three months is a little early for most stem cell transplant recipients, because they don’t have a fully functional immune system yet,” Chemaly says. “But we don’t want them to wait any longer, because they’re already at higher risk of developing complications if they catch COVID-19.”

Patients should try to obtain the same brand of vaccine they did originally — whether it’s Johnson & Johnson’s Janssen single-dose shot, or both doses of a two-dose mRNA regimen from either Pfizer/BioNTech or Moderna.

“You never know how people are going to react to something,” Chemaly notes. “But if you did fine with it the first time, there’s no reason to believe that you’ll respond any differently now.”

Plan to receive the recommended third dose, if needed

Anyone who’s been re-vaccinated with the Moderna or Pfizer vaccine, whether due to a stem cell transplant or a CAR T cell therapy, should also plan on receiving the recommended third dose 28 days later. Anyone who gets revaccinated with the J&J vaccine should plan to get the booster shot two months later. Talk to your care team about the best time to receive it.

“If your immune system is slow to respond, it may not be able to mount an adequate defense against COVID-19,” says Chemaly. “When patients need steroids to reduce certain side effects, it can suppress their immune systems even more. So, it may take you even longer to recover, and to respond robustly to any given vaccine.”

Request an appointment at MD Anderson online or by calling 1-877-632-6789.

Last updated Jan. 12, 2022

COVID-19 boosters have now been approved for all adults. This is welcome news for many who are eager to get added protection against COVID-19.

To help cut through the confusion about COVID-19 vaccine booster shots, we asked infectious diseases specialist and head of Internal Medicine David Tweardy, M.D. , to answer common questions.

Who can get a booster shot?

The Centers for Disease Control and Prevention (CDC) recommends that all eligible adults get a COVID-19 vaccine booster shot. The Food and Drug Administration (FDA) expanded the emergency use authorization for both the two-dose Pfizer and Moderna COVID-19 vaccine series to include booster shots for all adults. Individuals ages 18 and older can get the Moderna booster, and individuals ages 12 and older can get the Pfizer booster.

Additionally, anyone age 18 or older who received Johnson & Johnson's Janssen COVID-19 vaccine is eligible to get a booster shot.

When can I get a booster shot?

If you received the Pfizer or Moderna two-dose series, you should get a booster dose five months after you received your second dose.

If you received the single-dose J&J vaccine, you can get a booster dose two months after receiving your initial vaccine.

If I got the Pfizer or Moderna vaccine series, can I get my booster shot sooner than five months after I got my last vaccine dose? Why do I need to wait until five months after the second dose?

The mRNA vaccines provide great protection against severe COVID-19 infection, but after about five months that protection may wane a little.

There’s not a benefit to getting the booster sooner, but once you’re eligible and have reached that five-month mark, it’s time to consider getting a booster.

Are the booster shots different than the original vaccines? How will a booster help protect against the delta variant and any new, emerging variants?

The same formulation is used for all vaccine doses. The Pfizer and J&J boosters are the same dose as the original vaccines; the Moderna booster dose is half the dosage of the original vaccine.

The hope is that a booster shot will help amp up your body’s immune response so it can better protect against COVID-19, even as new variants emerge.

Earlier this year, we heard a lot about third doses of COVID-19 vaccine. Are booster shots and additional doses the same thing?

Not exactly. In August, additional COVID-19 doses – also called third doses – became available for moderately and severely immunocompromised individuals. This is a third dose that comes after the initial two-dose vaccine series of the for Pfizer-BioNTech’s or Moderna vaccine for people who may not have mounted a strong enough immune response after receiving the initial vaccine series. Since these individuals have weakened immune systems, they need that third dose to protect against COVID-19 since they may not have had the same level of protection against COVID-19 as other people.

A booster dose, on the other hand, is a subsequent dose given months after the initial vaccination to reinvigorate the immune system. Booster doses are intended for people whose immune response against COVID-19 may have decreased over time.

How long do I need to wait between my booster and other vaccines, such as the flu vaccine?

There’s no need to space out your booster shot and flu vaccine. The CDC says you can safely get other vaccines without regard to timing with the COVID-19 vaccine.

This flu season is expected to be a bad one, and we are still dealing with the highly transmissible delta variant. So, it’s important to get both your flu vaccine, and, if you’re eligible, COVID-19 booster as soon as possible.

When will I need another booster after this?

Researchers are looking closely at the data on vaccines, but it is not yet known whether more booster shots will be needed in the future.

How long after I get the booster will it take until I have the maximum protection against COVID-19?

You'll have full protection about two weeks after you receive the vaccine booster dose.

What if I don’t get the booster – or I wait to get one? What are the risks?

Immunity to COVID-19 has been shown to wane a little bit over time. That means you’re potentially at increased risk for getting a COVID-19 breakthrough infection.

Getting your booster shot once you’re eligible will play a vital role in reducing your risk of COVID-19. The delta variant has shown us that we can’t let our guards down and need to do everything we can to protect ourselves and each other – including immunocompromised individuals like our cancer patients at MD Anderson.

Do I need to get the same vaccine for the booster that I got for the first two doses? And do I need to get it at the same place I got the first two doses?

For those who are eligible for a booster, you have the option to receive any of the three boosters (Moderna, Pfizer or J&J). However, it's best to talk to your health care provider to weigh the risks and benefits of mixing and matching vaccines.

You do not need to get your booster at the same place you got the first two doses. But make sure you take your vaccination record with you when you get vaccinated to show which vaccine you received originally and when.

Does MD Anderson offer booster shots?

Yes. MD Anderson patients can schedule a Pfizer or Moderna booster shot through MyChart. Family members and members of the community can schedule a COVID-19 booster online.

MD Anderson does not have a supply of J&J vaccines at this time.

Will I have to keep masking and social distancing once I get a COVID-19 booster?

For now, it is important to continue masking and physical distancing even after you get a booster. But the hope is that as more people get vaccinated and get boosters, it will be safe to ease up on some of these precautions.

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Mixing and matching COVID-19 vaccines: Should you do it?
5 things to know about the FDA approval process

Request an appointment at MD Anderson online or by calling 1-877-632-6789.

The box containing the first 4,875 COVID-19 vaccine doses to arrive at MD Anderson was much larger than I’d expected. It only had five small trays of vials inside, but with all of the insulation and dry ice needed to keep them frozen, it weighed about 80 pounds.

I remember being very nervous as the delivery truck backed up to our loading dock on Dec. 14, 2020. MD Anderson was the first hospital in the Texas Medical Center to get the vaccine. And though we’d been planning for its arrival for a couple of weeks, all I could think was, “What if we missed a step? Do we have everything ready?”

Once the vaccines were safely in our freezer, we all breathed a big sigh of relief. But I must have checked on that freezer about 30 times. After watching the devastation wrought by the coronavirus unfold in real-time, there was a real sense of pressure to execute our vaccine plan.

The next day, we did a trial run to work out the kinks in our distribution process. We vaccinated several frontline employees with a high risk of occupational exposure. MD Anderson’s Chief Infection Control Officer Roy Chemaly, M.D., was the first one to receive the COVID-19 vaccine.

A chill ran up my spine as I watched the first few people getting their shots. I knew I was witnessing history. And it was pretty exciting to be a part of that.

There was also a sense of satisfaction in seeing all of our preparations come full circle. I’ve been at MD Anderson for about seven years, and collaboration is a part of who we are. It’s something we do every day. But this effort took teamwork to a whole different level by requiring multidisciplinary planning and strong communication.

So many people were invested in this vaccine campaign — not just for our patients and employees, but also for our loved ones and the community as a whole. It was thrilling to see so many people coming together — and literally rolling up their sleeves for the collective good. We knew that everyone was waiting for this and hoping it would help make strides to end the pandemic. So, we were not going to fail.

I am happy to say that we have been successful since day one.

Stefani Gautreaux is inpatient manager in Pharmacy Operations at MD Anderson.

Request an appointment at MD Anderson online or by calling 1-877-632-6789.

Last updated Oct. 25 2021

Research studies show that immunocompromised people who have low or no protection following two doses of mRNA COVID-19 vaccines may have an improved response after an additional dose of the same vaccine.

Based on this research, certain immunocompromised individuals, including certain cancer patients and survivors, can receive a third vaccine dose in order to strengthen their immune system’s response against COVID-19. But who is actually eligible for a third dose? And what can you expect if you or a loved one needs one?

To answer common questions about third COVID-19 vaccine doses, we spoke with infectious diseases specialist and head of Internal Medicine David Tweardy, M.D.

What is the difference between a third dose and a booster shot of COVID-19 vaccine?

An additional dose – also called a third dose – follows the initial two-dose vaccine series for people who may not have mounted a strong enough immune response after receiving the initial vaccine series. In other words, these individuals may not have had the same level of protection against COVID-19 as other individuals due to their weakened immune systems, so they need additional protection that can be provided by a third dose.

The FDA and Centers for Disease Control and Prevention (CDC) have authorized additional doses of Pfizer and Moderna’s COVID-19 vaccines for severely immunocompromised individuals.

By contrast, a booster dose is a supplemental dose given to groups whose immune response has waned over time.

Is the vaccine you receive for the third dose different than the vaccine people will receive for the booster?

According to the FDA, the same formulation is used for these vaccines. However, individuals that receive a Moderna booster receive a dosage half the size of the original dose; the Pfizer booster, on the other hand, is the same dose as the first two vaccines.

The Delta variant is highly transmissible and immunocompromised individuals may not have built up a strong immune response after the first two doses, it’s important to go ahead and get the third dose if you’re eligible. The hope is that will help strengthen your body’s immune response against COVID-19.

Who is eligible for a third dose of the COVID-19 vaccines?

People eligible for an additional COVID-19 vaccine dose include those who received the two-dose Moderna or Pfizer COVID-19 vaccine series and are moderately or severely immunocompromised, such as those with certain conditions identified by the CDC.

Examples include:

• Active or recent cancer treatment. Recent includes within one year of completing immunosuppressive therapy.
• Solid-organ transplant
• CAR T cell therapy 
• Autologous or allogeneic hematopoietic stem cell transplant within the last two years, or beyond two years for patients with chronic graft vs. host disease (GVHD), and/or ongoing immunosuppression
• History of primary immunodeficiency
• Advanced or untreated HIV infection
• People on active immunosuppressive therapy, such as chemotherapy, radiation therapy, high-dose corticosteroids, alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, tumor-necrosis factor (TNF) blockers, certain biologic agents (e.g., rituximab) and other biologic agents that are immunosuppressive or immunomodulatory.

Do I need to get the same type of vaccine for my third dose as I got for the first two? For instance, if I got the Pfizer vaccine before, do I need to get the Pfizer vaccine again?

The CDC recommends that a third dose of the same mRNA vaccine be used, whenever available, for people who received either the Pfizer or Moderna COVID-19 vaccine series. If you’re not sure which mRNA vaccine you got or aren’t able to get the same vaccine, it’s OK to get either the Pfizer or Moderna mRNA COVID-19 vaccine.

What if I got the one-dose Johnson & Johnson vaccine? Do I need to another dose, or can I get the Pfizer or Moderna two-dose series?

The FDA has authorized a second dose of the Johnson & Johnson’s Janssen COVID-19 vaccine provides improved antibody response in immunocompromised people. The FDA’s authorization for additional doses only applies to the two mRNA COVID-19 vaccines. The FDA and CDC are working to provide guidance on this issue.

When should eligible cancer patients get a third dose?

People with moderately to severely compromised immune systems can receive an additional dose at least 28 days after their second dose of the Pfizer or Moderna COVID-19 vaccine.

However, patients currently receiving chemotherapy, immunotherapy, CAR T cells, stem cell transplants or participating in clinical trials may need to coordinate timing of their additional vaccine dose with their treatment schedule to optimize their vaccine response. Talk to your primary health care provider to determine the appropriate timing for your additional vaccination dose if you are immunocompromised or taking immunosuppressive therapies.

Can childhood cancer patients get a third dose?

Yes. Adolescents ages 12-17 years are eligible to receive the Pfizer COVID-19 vaccine. Those younger than age 18 are not authorized to receive the Moderna vaccine, and children younger than age 12 years are not authorized to receive any COVID-19 vaccine at this time.

What are the most common side effects of the third dose?

Reactions reported after the third mRNA dose are similar to what people experienced after receiving the two-dose series. The most commonly reported side effects are fatigue and pain at injection site. Most post-vaccination symptoms are mild to moderate and resolve within 1-2 days.

Do I need antibody testing to receive an additional vaccine dose?

No. Outside the context of research studies, the CDC does not recommend antibody testing to determine an immune response to vaccination. In many cases, you may have a negative antibody test result even if you are fully vaccinated.

What precautions do cancer patients need to take after receiving a third dose?

People who are immunocompromised may continue to experience a reduced immune response to COVID-19 vaccines, even after receiving the third dose. It is important to continue following COVID-19 safety precautions, including wearing a mask in indoor public settings, staying apart from others who are not from your household, and avoiding crowds and poorly ventilated indoor spaces. Because the delta variant is highly contagious, social distancing and wearing high-quality KF-94 or KN-95 mask may offer better protection.

It is also important to encourage your family, friends and anyone you spend time with to get vaccinated.

Will we need additional doses or boosters after this third dose?

This is something researchers are still looking at. They hope to gain a better understanding of whether future doses or boosters will be needed and, if so, how frequently.

Is MD Anderson offering the third dose of COVID-19 vaccines?

Yes. Eligible MD Anderson patients can sign into MyChart to schedule an appointment; you will need to bring your proof of prior vaccination and attest that you meet criteria for immunocompromised conditions. We are unable to accept walk-ins.

Appointments for community members who are eligible for a third dose of the vaccine will be available at MD Anderson soon.

Can I get the third dose somewhere else if it’s more convenient?

Yes. People who meet the eligibility criteria for additional COVID-19 doses should consider getting vaccinated wherever they can. Use the National Vaccine Finder to see appointments available in your community. Again, talk to your primary health care provider to determine the appropriate timing for your additional vaccination dose if you are immunocompromised or taking immunosuppressive therapies.

What is your advice to immunocompromised individuals who don’t want to get a third dose, either because they’ve already had COVID-19 or don’t want to get another shot?

Talk to your doctor about these concerns, but it’s really important to get the third dose if you are immunocompromised. The latest research indicates the COVID-19 vaccines are safe and effective, but their effectiveness may wane over time and/or they may become less effective with new variants. In addition, an immunocompromised individual may not have had a sufficient immune response to their initial vaccine series or infection; a third dose has been shown to improve immunity in those who have received a complete vaccine series, and it is expected to improve immunity in those who had a COVID-19 infection.