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.

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

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.

You may have heard talk recently about a second COVID-19 vaccine booster shot. But if you’re confused about whether you need one — and what it is — you’re not alone.

We checked in with Chief Infection Control Officer Roy Chemaly, M.D., to learn about eligibility requirements, timing and which type of booster shot is best.

So, who needs a second COVID-19 booster shot?

Anyone age 50 or older, or anyone age 12 or older who has an underlying health condition that compromises their immune system. Both of these groups are eligible for a second booster shot and should seriously consider getting one.

Isn’t a booster shot the same thing as a third dose?

Not exactly. The Pfizer/BioNTech booster contains the same amount of vaccine as each shot held in the original vaccination series. The Moderna booster contains only half the original amount.

A third dose is identical to the first or second dose of a Pfizer or Moderna vaccine; it contains the exact same amount. Third doses are recommended for severely immunocompromised individuals, since their bodies may not have responded as robustly as the average person’s to the two-dose series.

Let’s say I’m immunocompromised and I’ve already had three full doses and a COVID-19 booster shot. Does this mean I need another booster?

If you’re immunocompromised, you are eligible to receive up to five shots:

• the original two-dose series of either the Pfizer or Moderna mRNA vaccines
• a third dose, according to the CDC’s timing recommendations
• a first booster shot (no earlier than 3 months after the third dose)
• a second booster shot (no earlier than 4 months after the first booster shot)

So, as of right now, you could receive five shots in all.  

Is it better to get a second booster shot now, or wait until another COVID-19 variant emerges and/or researchers complete clinical trials with updated vaccines? 

Why wait? If and when another COVID-19 variant might emerge is impossible to predict. It may or may not ever happen. But waning immunity is real. And it’s happening right now. So, you can still get COVID-19, especially if you’re at high risk. The pandemic isn’t over yet. That’s why I say, do it now. That way, you’ll be as protected as possible if another variant does arise.

Is it OK to mix and match my COVID-19 vaccines?

My personal preference is to stick with the same type of vaccine you initially received, if it’s available. And the CDC recommends choosing one of the mRNA vaccines (Pfizer or Moderna) for your first booster shot in most cases.

But it’s fine to mix and match vaccines between your initial series/single-shot regimen and your first booster. The data show no difference in efficacy or safety between people who consistently received their vaccines from one manufacturer and those who mixed and matched their vaccines.

That being said, the second booster shot MUST be one of the mRNA vaccines — either Pfizer or Moderna — because we have no data yet on the efficacy or safety of additional doses for the Johnson & Johnson/Janssen vaccine from the Food & Drug Administration (FDA).

What’s the one thing you want people to know about booster shots?

We’re actually not doing too well nationally, in terms of people getting their COVID-19 booster shots. Getting vaccinated, we’ve accomplished quite a bit, at least when it comes to health care workers. So, right now, it’s all about boosting.

The value of getting boosted is undeniable: it’s already proven to increase immunity, decrease transmission rates, and reduce the overall chances of severe infection, hospitalization and death. That’s why I would encourage everyone to get boosted at least once.

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.